diff --git a/Cargo.toml b/Cargo.toml
index 53e6345..7714021 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -4,4 +4,4 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
-rand = "0.8.5"
+rand = { version = "0.8.5", features = ["small_rng"] }
diff --git a/src/game.rs b/src/game.rs
new file mode 100644
index 0000000..931cc08
--- /dev/null
+++ b/src/game.rs
@@ -0,0 +1,168 @@
+use rand::{seq::SliceRandom, Rng};
+
+pub trait Player {
+    fn select_card(
+        &self,
+        hand: &[Card],
+        stack: &[Card],
+        additional_information: &AdditionalInformation,
+    ) -> Card;
+}
+
+#[derive(Debug)]
+pub struct AdditionalInformation {}
+
+#[derive(Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub enum Color {
+    Clubs,
+    Spades,
+    Hearts,
+    Diamonds,
+}
+
+impl Color {
+    fn get_symbol(&self) -> char {
+        match self {
+            Color::Clubs => '♣',
+            Color::Spades => '♠',
+            Color::Hearts => '♥',
+            Color::Diamonds => '♦',
+        }
+    }
+}
+
+#[derive(Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
+pub struct Card {
+    pub color: Color,
+    pub value: u8,
+}
+
+impl std::fmt::Debug for Card {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}{}", self.color.get_symbol(), self.get_value_char())
+    }
+}
+
+impl Card {
+    fn new(color: Color, value: u8) -> Self {
+        Self { color, value }
+    }
+
+    fn cost(&self) -> u8 {
+        match self.color {
+            Color::Spades => {
+                if self.value == 6 {
+                    4
+                } else {
+                    0
+                }
+            }
+            Color::Hearts => 1,
+            _ => 0,
+        }
+    }
+
+    fn get_value_char(&self) -> &'static str {
+        match self.value {
+            1 => "7",
+            2 => "8",
+            3 => "9",
+            4 => "10",
+            5 => "J",
+            6 => "Q",
+            7 => "K",
+            8 => "A",
+            _ => unreachable!(),
+        }
+    }
+}
+
+pub fn playeble(card: Card, hand: &[Card], stack_color: Option<Color>) -> bool {
+    if let Some(stack_color) = stack_color {
+        stack_color == card.color || hand.iter().all(|c| c.color != stack_color)
+    } else {
+        true
+    }
+}
+
+pub fn herzen(player: &[Box<dyn Player>], starting_player: usize, rng: &mut impl Rng) -> Vec<u8> {
+    let mut full_deck = (1..=8)
+        .flat_map(|u| {
+            [
+                Card::new(Color::Clubs, u),
+                Card::new(Color::Spades, u),
+                Card::new(Color::Hearts, u),
+                Card::new(Color::Diamonds, u),
+            ]
+            .into_iter()
+        })
+        .collect::<Vec<_>>();
+
+    full_deck.shuffle(rng);
+
+    let hand_size = full_deck.len() / player.len();
+    let mut hands = (0..player.len())
+        .map(|i| full_deck[(hand_size * i)..(hand_size * (i + 1))].to_vec())
+        .collect::<Vec<_>>();
+
+    let mut round_starting_player = starting_player;
+
+    let mut points = vec![0; player.len()];
+
+    for i in 0..hand_size {
+        let mut stack = Vec::with_capacity(player.len());
+
+        println!("## Round {i}:");
+
+        for j in 0..player.len() {
+            let index = (round_starting_player + j) % player.len();
+
+            println!("# Player {index}");
+
+            let ai = AdditionalInformation {};
+
+            let played_card = player[index].select_card(&hands[index], &stack, &ai);
+
+            assert!(playeble(
+                played_card,
+                &hands[index],
+                stack.first().map(|c| c.color)
+            ));
+
+            let card_index = hands[index].iter().position(|&c| c == played_card).unwrap();
+
+            hands[index].remove(card_index);
+
+            println!("# Player {index} played {played_card:?}");
+            stack.push(played_card);
+        }
+
+        let winner = (player.len()
+            + stack
+                .iter()
+                .enumerate()
+                .max_by_key(|(_, &c)| {
+                    if c.color == stack[0].color {
+                        c.value
+                    } else {
+                        0
+                    }
+                })
+                .unwrap()
+                .0
+            - round_starting_player)
+            % player.len();
+
+        let cost = stack.iter().map(|c| c.cost()).sum::<u8>();
+
+        println!("## Player {winner} takes the stack {stack:?} with {cost} points.");
+
+        points[winner] += cost;
+
+        round_starting_player = winner;
+    }
+
+    println!("## Game ended. Points: {points:?}");
+
+    points
+}
diff --git a/src/main.rs b/src/main.rs
index 6eddbcc..4edf67b 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,224 +1,133 @@
-use rand::seq::SliceRandom;
+use game::Player;
+use rand::{rngs::SmallRng, SeedableRng};
 
-#[derive(Clone, Copy, Hash, PartialEq, Eq)]
-struct Card {
-    color: Color,
-    value: u8,
-}
+mod game;
+mod player;
 
-impl std::fmt::Debug for Card {
-    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
-        write!(f, "{}{}", self.color.get_symbol(), self.get_value_char())
-    }
-}
+// #[derive(Debug, Clone)]
+// enum Knowledge {
+//     Full(Vec<Card>),
+//     Partial([bool; 4]),
+// }
 
-impl Card {
-    fn new(color: Color, value: u8) -> Self {
-        Self { color, value }
-    }
+// fn solve(
+//     current: usize,
+//     knowledge: &[Knowledge],
+//     unseen: &[Card],
+//     stack: &mut Vec<Card>,
+//     remaining: usize,
+// ) -> Vec<f64> {
+//     let num_player = knowledge.len();
+//     if remaining == 0 {
+//         vec![0.0; num_player]
+//     } else if stack.len() == num_player {
+//         let first_card = stack.first().unwrap();
 
-    fn cost(&self) -> u8 {
-        match self.color {
-            Color::Spades => {
-                if self.value == 6 {
-                    4
-                } else {
-                    0
-                }
-            }
-            Color::Hearts => 1,
-            _ => 0,
-        }
-    }
+//         let winning_card = stack
+//             .iter()
+//             .enumerate()
+//             .max_by_key(|g| {
+//                 if g.1.color == first_card.color {
+//                     g.1.value
+//                 } else {
+//                     0
+//                 }
+//             })
+//             .unwrap();
 
-    fn get_value_char(&self) -> &'static str {
-        match self.value {
-            1 => "7",
-            2 => "8",
-            3 => "9",
-            4 => "10",
-            5 => "J",
-            6 => "Q",
-            7 => "K",
-            8 => "A",
-            _ => unreachable!(),
-        }
-    }
-}
+//         let winning_player = (current + winning_card.0) % num_player;
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash)]
-enum Color {
-    Clubs,
-    Spades,
-    Hearts,
-    Diamonds,
-}
+//         let cost = stack.iter().map(|c| c.cost()).sum::<u8>();
 
-impl Color {
-    fn get_symbol(&self) -> char {
-        match self {
-            Color::Clubs => '♣',
-            Color::Spades => '♠',
-            Color::Hearts => '♥',
-            Color::Diamonds => '♦',
-        }
-    }
-}
+//         let mut new_stack = Vec::new();
+//         let mut s = solve(
+//             winning_player,
+//             knowledge,
+//             unseen,
+//             &mut new_stack,
+//             remaining - 1,
+//         );
+//         s[winning_player] += cost as f64;
+//         s
+//     } else {
+//         match &knowledge[current] {
+//             Knowledge::Full(cards) => {
+//                 let mut min: Option<Vec<f64>> = None;
+//                 let mut own_knowledge = knowledge.to_vec();
+//                 if let Some(first_card) = stack.first().copied() {
+//                     for i in 0..cards.len() {
+//                         if cards[i].color == first_card.color {
+//                             stack.push(cards[i]);
 
-#[derive(Debug, Clone)]
-enum Knowledge {
-    Full(Vec<Card>),
-    Partial([bool; 4]),
-}
+//                             own_knowledge[current] = Knowledge::Full(
+//                                 cards
+//                                     .iter()
+//                                     .enumerate()
+//                                     .filter(|(j, _)| j != &i)
+//                                     .map(|(_, &c)| c)
+//                                     .collect(),
+//                             );
+//                             let m = solve(
+//                                 (current + 1) % num_player,
+//                                 &own_knowledge,
+//                                 unseen,
+//                                 stack,
+//                                 remaining,
+//                             );
+//                             if let Some(min) = &mut min {
+//                                 if m[current] < min[current] {
+//                                     *min = m;
+//                                 }
+//                             } else {
+//                                 min = Some(m);
+//                             }
+//                             stack.pop();
+//                         }
+//                     }
+//                 }
+//                 if let Some(m) = min {
+//                     m
+//                 } else {
+//                     let mut min = vec![f64::INFINITY; num_player];
+//                     for i in 0..cards.len() {
+//                         stack.push(cards[i]);
+//                         own_knowledge[current] = Knowledge::Full(
+//                             cards
+//                                 .iter()
+//                                 .enumerate()
+//                                 .filter(|(j, _)| j != &i)
+//                                 .map(|(_, &c)| c)
+//                                 .collect(),
+//                         );
 
-fn solve(
-    current: usize,
-    knowledge: &[Knowledge],
-    unseen: &[Card],
-    stack: &mut Vec<Card>,
-    remaining: usize,
-) -> Vec<f64> {
-    let num_player = knowledge.len();
-    if remaining == 0 {
-        vec![0.0; num_player]
-    } else if stack.len() == num_player {
-        let first_card = stack.first().unwrap();
+//                         let m = solve(
+//                             (current + 1) % num_player,
+//                             &own_knowledge,
+//                             unseen,
+//                             stack,
+//                             remaining,
+//                         );
+//                         if m[current] < min[current] {
+//                             min = m;
+//                         }
+//                         stack.pop();
+//                     }
 
-        let winning_card = stack
-            .iter()
-            .enumerate()
-            .max_by_key(|g| {
-                if g.1.color == first_card.color {
-                    g.1.value
-                } else {
-                    0
-                }
-            })
-            .unwrap();
-
-        let winning_player = (current + winning_card.0) % num_player;
-
-        let cost = stack.iter().map(|c| c.cost()).sum::<u8>();
-
-        let mut new_stack = Vec::new();
-        let mut s = solve(
-            winning_player,
-            knowledge,
-            unseen,
-            &mut new_stack,
-            remaining - 1,
-        );
-        s[winning_player] += cost as f64;
-        s
-    } else {
-        match &knowledge[current] {
-            Knowledge::Full(cards) => {
-                let mut min: Option<Vec<f64>> = None;
-                let mut own_knowledge = knowledge.to_vec();
-                if let Some(first_card) = stack.first().copied() {
-                    for i in 0..cards.len() {
-                        if cards[i].color == first_card.color {
-                            stack.push(cards[i]);
-
-                            own_knowledge[current] = Knowledge::Full(
-                                cards
-                                    .iter()
-                                    .enumerate()
-                                    .filter(|(j, _)| j != &i)
-                                    .map(|(_, &c)| c)
-                                    .collect(),
-                            );
-                            let m = solve(
-                                (current + 1) % num_player,
-                                &own_knowledge,
-                                unseen,
-                                stack,
-                                remaining,
-                            );
-                            if let Some(min) = &mut min {
-                                if m[current] < min[current] {
-                                    *min = m;
-                                }
-                            } else {
-                                min = Some(m);
-                            }
-                            stack.pop();
-                        }
-                    }
-                }
-                if let Some(m) = min {
-                    m
-                } else {
-                    let mut min = vec![f64::INFINITY; num_player];
-                    for i in 0..cards.len() {
-                        stack.push(cards[i]);
-                        own_knowledge[current] = Knowledge::Full(
-                            cards
-                                .iter()
-                                .enumerate()
-                                .filter(|(j, _)| j != &i)
-                                .map(|(_, &c)| c)
-                                .collect(),
-                        );
-
-                        let m = solve(
-                            (current + 1) % num_player,
-                            &own_knowledge,
-                            unseen,
-                            stack,
-                            remaining,
-                        );
-                        if m[current] < min[current] {
-                            min = m;
-                        }
-                        stack.pop();
-                    }
-
-                    min
-                }
-            }
-            Knowledge::Partial(_) => todo!(),
-        }
-    }
-}
+//                     min
+//                 }
+//             }
+//             Knowledge::Partial(_) => todo!(),
+//         }
+//     }
+// }
 
 fn main() {
-    let mut full_deck = (1..=8)
-        .flat_map(|u| {
-            [
-                Card::new(Color::Clubs, u),
-                Card::new(Color::Spades, u),
-                Card::new(Color::Hearts, u),
-                Card::new(Color::Diamonds, u),
-            ]
-            .into_iter()
-        })
-        .collect::<Vec<_>>();
+    let player: [Box<dyn Player>; 2] = [
+        Box::new(player::highest::Highest {}),
+        Box::new(player::highest::Highest {}),
+    ];
 
-    let mut rng = rand::thread_rng();
+    let mut rng = SmallRng::from_entropy();
 
-    full_deck.shuffle(&mut rng);
-
-    let cards = 4;
-    let player = 4;
-
-    let mut knowledge = Vec::new();
-
-    for i in 0..player {
-        knowledge.push(Knowledge::Full(
-            full_deck[cards * i..cards * (i + 1)].to_vec(),
-        ));
-    }
-
-    dbg!(&knowledge);
-
-    let unseen = [];
-
-    let mut stack = Vec::new();
-
-    let start = std::time::Instant::now();
-    let r = solve(0, &knowledge, &unseen, &mut stack, cards);
-
-    dbg!(start.elapsed());
-    dbg!(r);
+    game::herzen(&player, 0, &mut rng);
 }
diff --git a/src/player/mod.rs b/src/player/mod.rs
new file mode 100644
index 0000000..a8201a6
--- /dev/null
+++ b/src/player/mod.rs
@@ -0,0 +1,60 @@
+pub mod cli {
+
+    use crate::game::{playeble, Player};
+
+    pub struct Cli {}
+
+    impl Player for Cli {
+        fn select_card(
+            &self,
+            hand: &[crate::game::Card],
+            stack: &[crate::game::Card],
+            additional_information: &crate::game::AdditionalInformation,
+        ) -> crate::game::Card {
+            let mut h = hand.to_vec();
+
+            h.sort();
+            println!("hand:      {:?}", h);
+
+            h.retain(|&c| playeble(c, hand, stack.first().map(|d| d.color)));
+
+            println!("playeble:  {:?}", h);
+            println!("stack:     {:?}", stack);
+            println!("additional information: {:?}", additional_information);
+
+            let mut buffer = String::new();
+
+            let _ = std::io::stdin().read_line(&mut buffer);
+
+            let index = buffer.trim().parse::<usize>().unwrap();
+
+            h[index]
+        }
+    }
+}
+
+pub mod highest {
+    use std::cmp::Reverse;
+
+    use crate::game::{playeble, Player};
+
+    pub struct Highest {}
+
+    impl Player for Highest {
+        fn select_card(
+            &self,
+            hand: &[crate::game::Card],
+            stack: &[crate::game::Card],
+            additional_information: &crate::game::AdditionalInformation,
+        ) -> crate::game::Card {
+            let _ = additional_information;
+            let mut hand = hand.to_vec();
+
+            hand.sort_by_key(|c| Reverse(*c));
+            *hand
+                .iter()
+                .find(|&&c| playeble(c, &hand, stack.first().map(|d| d.color)))
+                .unwrap()
+        }
+    }
+}