diff --git a/4.shellSort.md b/4.shellSort.md
index cfa59f5..e1e99a3 100644
--- a/4.shellSort.md
+++ b/4.shellSort.md
@@ -69,7 +69,7 @@ def shellSort(arr):
 func shellSort(arr []int) []int {
 	length := len(arr)
 	gap := 1
-	for gap < gap/3 {
+	for gap < length/3 {
 		gap = gap*3 + 1
 	}
 	for gap > 0 {