diff --git a/2018/day01.rb b/2018/day01.rb
new file mode 100644
index 0000000..8bffc18
--- /dev/null
+++ b/2018/day01.rb
@@ -0,0 +1,16 @@
+nums = STDIN.read.split("\n").map(&:to_i)
+puts nums.sum
+
+def part2(nums)
+  seen = Set.new
+  sum = 0
+  loop do
+    nums.each do |num|
+      return sum if seen.include?(sum)
+      seen.add(sum)
+      sum += num
+    end
+  end
+end
+
+puts part2(nums)
diff --git a/2018/examples/day01.txt b/2018/examples/day01.txt
new file mode 100644
index 0000000..e5c174f
--- /dev/null
+++ b/2018/examples/day01.txt
@@ -0,0 +1,6 @@
++1
+-2
++3
++1
++1
+-2