diff --git a/2021/04/README.md b/2021/04/README.md
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+# 04
+
+<details>
+  <summary>Solutions</summary>
+  <ol>
+    <li>8580</li>
+    <li>9576</li>
+  </ol>
+</details>
diff --git a/2021/04/python/main.py b/2021/04/python/main.py
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+#!/usr/bin/env python
+
+from os.path import join, dirname
+from typing import List
+
+# Day 04
+
+# Common
+
+
+def read_input(filename):
+    data = join(dirname(__file__), '..', filename)
+    with open(data) as f:
+        return f.read().strip()
+
+
+test = read_input('test.txt')
+data = read_input('input.txt')
+
+
+class Board:
+    def __init__(self, raw: str) -> None:
+        self.matrix = [
+            [int(x) for x in row.split(' ') if x != '']
+            for row in raw.split('\n')
+        ]
+        self.chosen = [
+            [False for _ in range(len(self.matrix))]
+            for _ in range(len(self.matrix))
+        ]
+
+    def enter(self, number: int):
+        for i, row in enumerate(self.matrix):
+            for j, col in enumerate(row):
+                if col == number:
+                    self.chosen[i][j] = True
+
+    def bingo(self):
+        for row in self.chosen:
+            if all(row):
+                return True
+        for i in range(len(self.chosen)):
+            if all([row[i] for row in self.chosen]):
+                return True
+        return False
+
+    def flag(self, number: int) -> int:
+        numbers = []
+        for i, row in enumerate(self.chosen):
+            for j, col in enumerate(row):
+                if not col:
+                    numbers.append(self.matrix[i][j])
+        total = sum(numbers)
+        # print(f'Flag: {total} {number}')
+        return total*number
+
+    def __str__(self):
+        numbers = '\n'.join([' '.join([str(x) for x in row])
+                            for row in self.matrix])
+        chosen = '\n'.join([' '.join([str(x) for x in row])
+                           for row in self.chosen])
+        return f'{numbers}\n{chosen}'
+
+
+class Bingo:
+    def __init__(self, raw: str) -> None:
+        numbers, *boards = raw.split('\n\n')
+        self.dice = [int(x) for x in numbers.strip().split(',')]
+        self.boards = [Board(board) for board in boards]
+
+    def play(self, to_win=True):
+        for number in self.dice:
+            finished: List[Board] = []
+            for board in self.boards:
+                board.enter(number)
+                if board.bingo():
+                    if to_win:
+                        return board.flag(number)
+                    else:
+                        if len(self.boards) == 1:
+                            return board.flag(number)
+                        else:
+                            finished.append(board)
+            if finished:
+                for board in finished:
+                    self.boards.remove(board)
+
+    def __str__(self):
+        return '\n\n'.join([str(board) for board in self.boards])
+
+
+# 1
+print('1.')
+
+bingo = Bingo(test)
+result = bingo.play()
+print(f"Test: {result}")
+
+bingo = Bingo(data)
+result = bingo.play()
+print(f"Result: {result}")
+
+
+# 2
+print('2.')
+
+bingo = Bingo(test)
+result = bingo.play(to_win=False)
+print(f"Test: {result}")
+
+bingo = Bingo(data)
+result = bingo.play(to_win=False)
+print(f"Result: {result}")