diff --git a/algorithm/sliding_window.py b/algorithm/sliding_window.py
index 222dec1..214b8bc 100644
--- a/algorithm/sliding_window.py
+++ b/algorithm/sliding_window.py
@@ -22,7 +22,7 @@ def sliding_window_template_with_examples(s, p):
 
     # loop the source string from begin to end
     while end < len(s):
-        counter[s[end]] += 1
+        counter[s[end]] -= 1
         # update count based on some condition
         if counter[s[end]] > 1:
             count += 1
@@ -49,4 +49,4 @@ def sliding_window_template_with_examples(s, p):
     return res
 
 
-# refer to https://leetcode.com/problems/minimum-window-substring/discuss/26808/here-is-a-10-line-template-that-can-solve-most-substring-problems
\ No newline at end of file
+# refer to https://leetcode.com/problems/minimum-window-substring/discuss/26808/here-is-a-10-line-template-that-can-solve-most-substring-problems