diff --git a/day21.py b/day21.py
new file mode 100644
index 0000000..e0322d2
--- /dev/null
+++ b/day21.py
@@ -0,0 +1,56 @@
+from tools.aoc import AOCDay
+from typing import Any
+
+
+class Day(AOCDay):
+    test_solutions_p1 = [739785]
+    test_solutions_p2 = [444356092776315]
+
+    def part1(self) -> Any:
+        pos = list(map(int, [x.split(": ")[1] for x in self.getInput()]))
+        scores = [0, 0]
+        target_score = 1000
+        rolls = 0
+        dice_roll = 0
+        while scores[0] < target_score and scores[1] < target_score:
+            for player in [0, 1]:
+                this_roll = 0
+                rolls += 3
+                for _ in range(3):
+                    dice_roll = 1 + (dice_roll % 100)
+                    this_roll += dice_roll
+
+                pos[player] = 1 + (this_roll + pos[player] - 1) % 10
+                scores[player] += pos[player]
+                if scores[player] >= target_score:
+                    break
+
+        return min(scores) * rolls
+
+    def roll_dirac(self, pos1, pos2, score1, score2, cache):
+        if (pos1, pos2, score1, score2) in cache:
+            return cache[(pos1, pos2, score1, score2)]
+        p1wins = 0
+        p2wins = 0
+        target_score = 21
+        for roll1 in range(3, 10):
+            tpos1 = 1 + (roll1 + pos1 - 1) % 10
+            if score1 + tpos1 >= target_score:
+                p1wins += 27
+            else:
+                for roll2 in range(3, 10):
+                    tpos2 = 1 + (roll2 + pos2 - 1) % 10
+                    if score2 + tpos2 >= target_score:
+                        p2wins += 27
+                    else:
+                        sub_p1wins, sub_p2wins = self.roll_dirac(tpos1, tpos2, score1 + tpos1, score2 + tpos2, cache)
+                        p1wins += sub_p1wins
+                        p2wins += sub_p2wins
+
+        cache[(pos1, pos2, score1, score2)] = p1wins, p2wins
+        return p1wins, p2wins
+
+    def part2(self) -> Any:
+        pos = list(map(int, [x.split(": ")[1] for x in self.getInput()]))
+        wins1, wins2 = self.roll_dirac(pos[0], pos[1], 0, 0, {})
+        return wins1, wins2
diff --git a/inputs/input21 b/inputs/input21
new file mode 100644
index 0000000..5ad5c4a
--- /dev/null
+++ b/inputs/input21
@@ -0,0 +1,2 @@
+Player 1 starting position: 7
+Player 2 starting position: 3
diff --git a/inputs/test_input21_1_0 b/inputs/test_input21_1_0
new file mode 100644
index 0000000..3f69194
--- /dev/null
+++ b/inputs/test_input21_1_0
@@ -0,0 +1,2 @@
+Player 1 starting position: 4
+Player 2 starting position: 8
diff --git a/inputs/test_input21_2_0 b/inputs/test_input21_2_0
new file mode 100644
index 0000000..3f69194
--- /dev/null
+++ b/inputs/test_input21_2_0
@@ -0,0 +1,2 @@
+Player 1 starting position: 4
+Player 2 starting position: 8