diff --git a/4/script.rb b/4/script.rb
new file mode 100755
index 0000000..0953448
--- /dev/null
+++ b/4/script.rb
@@ -0,0 +1,24 @@
+#!/usr/bin/env ruby
+
+require 'digest'
+
+def part1(input)
+  find_md5 input
+end
+
+def part2(input)
+  find_md5 input, 6
+end
+
+def find_md5(input, leading_zeros = 5)
+  (1..).detect do |i|
+    Digest::MD5.hexdigest(input + i.to_s).start_with?('0' * leading_zeros)
+  end
+end
+
+input = 'yzbqklnj'
+
+puts "=== Part 1 ==="
+puts part1(input)
+puts "=== Part 2 ==="
+puts part2(input)