diff --git a/2021/ruby/day_02.rb b/2021/ruby/day_02.rb
new file mode 100644
index 0000000..7e957f3
--- /dev/null
+++ b/2021/ruby/day_02.rb
@@ -0,0 +1,35 @@
+# h = 0
+# d = 0
+# ARGF.read.split("\n").map(&:split).each do |dir, n|
+#   n = n.to_i
+#   case dir
+#   when "forward"
+#     h += n
+#   when "down"
+#     d += n
+#   when "up"
+#     d -= n
+#   else
+#     fail dir
+#   end
+# end
+# p h, d, h*d
+
+h = 0
+d = 0
+aim = 0
+ARGF.read.split("\n").map(&:split).each do |dir, n|
+  n = n.to_i
+  case dir
+  when "forward"
+    h += n
+    d += aim * n
+  when "down"
+    aim += n
+  when "up"
+    aim -= n
+  else
+    fail dir
+  end
+end
+p h, d, h*d