diff --git a/2021/day01.rb b/2021/day01.rb
new file mode 100644
index 0000000..966a4b7
--- /dev/null
+++ b/2021/day01.rb
@@ -0,0 +1,7 @@
+measurements = STDIN.read.split("\n").map(&:to_i)
+
+def solve(measurements, size)
+  measurements.each_cons(size).map(&:sum).each_cons(2).count { |a, b| a < b }
+end
+puts solve(measurements, 1)
+puts solve(measurements, 3)
diff --git a/2021/examples/day01.txt b/2021/examples/day01.txt
new file mode 100644
index 0000000..167e291
--- /dev/null
+++ b/2021/examples/day01.txt
@@ -0,0 +1,10 @@
+199
+200
+208
+210
+200
+207
+240
+269
+260
+263