diff --git a/2018/internal/util/math.go b/2018/internal/util/math.go
new file mode 100644
index 0000000..a3bf4bc
--- /dev/null
+++ b/2018/internal/util/math.go
@@ -0,0 +1,8 @@
+package util
+
+func abs(x int) int {
+	if x < 0 {
+		return -x
+	}
+	return x
+}