diff --git a/2018/d05/ex1/ex1.py b/2018/d05/ex1/ex1.py
new file mode 100755
index 0000000..b93dfcb
--- /dev/null
+++ b/2018/d05/ex1/ex1.py
@@ -0,0 +1,29 @@
+#!/usr/bin/env python
+
+import sys
+
+
+def solve(input: str) -> int:
+    def reduce_polymer(polymer: str) -> str:
+        for i in range(26):
+            lower, upper = chr(ord("a") + i), chr(ord("A") + i)
+            polymer = polymer.replace(lower + upper, "")
+            polymer = polymer.replace(upper + lower, "")
+        return polymer
+
+    polymer = input.strip()
+    while True:
+        reduced = reduce_polymer(polymer)
+        if reduced == polymer:
+            return len(polymer)
+        polymer = reduced
+    assert False  # Sanity check
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()