diff --git a/2016/ruby/day_20.rb b/2016/ruby/day_20.rb
new file mode 100644
index 0000000..797ae4f
--- /dev/null
+++ b/2016/ruby/day_20.rb
@@ -0,0 +1,14 @@
+blacklist = ARGF.read.split("\n").map {|line| Range.new(*line.split(?-).map(&:to_i)) }
+
+ip = 0
+count = 0
+until ip > 4294967295
+  range = blacklist.find {|range| range.cover?(ip) }
+  if range.nil?
+    count += 1
+    ip += 1
+  else
+    ip = range.end + 1
+  end
+end
+puts count