diff --git a/2020/day17.py b/2020/day17.py
new file mode 100644
index 0000000..fb4550b
--- /dev/null
+++ b/2020/day17.py
@@ -0,0 +1,79 @@
+import sys
+
+
+def main():
+    lines = [line.rstrip() for line in sys.stdin]; sys.stdin = open("/dev/tty")
+
+    print("Actives:", part1(lines))
+    print("Hyperactives:", part2(lines))
+
+
+def part1(lines):
+    s = {}
+    for y, line in enumerate(lines):
+        for x, c in enumerate(line):
+            s[(x, y, 0)] = 1 if c == "#" else 0
+    for _ in range(6):
+        cycle(s)
+    return sum(s.values())
+
+
+def cycle(s):
+    future = {}
+    work_set = set(nn for x, y, z in s for nn in near(x, y, z))
+    for x, y, z in work_set:
+        an = 0
+        for nn in near(x, y, z):
+            an += s.get(nn, 0)
+        if (v := s.get((x, y, z), 0)) == 1 and not 2 <= an <= 3:
+            future[(x, y, z)] = 0
+        elif v == 0 and an == 3:
+            future[(x, y, z)] = 1
+    for f, fv in future.items():
+        s[f] = fv
+
+
+def near(x, y, z, include_self=False):
+    for zi in range(-1, 2):
+        for yi in range(-1, 2):
+            for xi in range(-1, 2):
+                if include_self or xi != 0 or yi != 0 or zi != 0:
+                    yield x + xi, y + yi, z + zi
+
+
+def part2(lines):
+    h = {}
+    for y, line in enumerate(lines):
+        for x, c in enumerate(line):
+            h[(x, y, 0, 0)] = 1 if c == "#" else 0
+    for _ in range(6):
+        cycle2(h)
+    return sum(h.values())
+
+
+def cycle2(h):
+    future = {}
+    work_set = set(nn for x, y, z, w in h for nn in hyper_near(x, y, z, w))
+    for x, y, z, w in work_set:
+        an = 0
+        for nn in hyper_near(x, y, z, w):
+            an += h.get(nn, 0)
+        if (v := h.get((x, y, z, w), 0)) == 1 and not 2 <= an <= 3:
+            future[(x, y, z, w)] = 0
+        elif v == 0 and an == 3:
+            future[(x, y, z, w)] = 1
+    for f, fv in future.items():
+        h[f] = fv
+
+
+def hyper_near(x, y, z, w, include_self=False):  # oh boy
+    for wi in range(-1, 2):
+        for zi in range(-1, 2):
+            for yi in range(-1, 2):
+                for xi in range(-1, 2):
+                    if include_self or xi != 0 or yi != 0 or zi != 0 or wi != 0:
+                        yield x + xi, y + yi, z + zi, w + wi
+
+
+if __name__ == "__main__":
+    main()