diff --git a/1.-pattern-sliding-window/1.0-introduction.md b/1.-pattern-sliding-window/1.0-introduction.md
index 76af1ea..e2a0ee1 100644
--- a/1.-pattern-sliding-window/1.0-introduction.md
+++ b/1.-pattern-sliding-window/1.0-introduction.md
@@ -106,7 +106,7 @@ public class Solution {
         //the length of the substring which match the target string.
         int len = Integer.MAX_VALUE; 
         
-        //loop at the begining of the source string
+        //loop at the beginning of the source string
         while(end < s.length()){
             
             char c = s.charAt(end);//get a character