diff --git a/378. Kth Smallest Element in a Sorted Matrix.md b/378. Kth Smallest Element in a Sorted Matrix.md
index 3c91ffe..c5b5110 100644
--- a/378. Kth Smallest Element in a Sorted Matrix.md	
+++ b/378. Kth Smallest Element in a Sorted Matrix.md	
@@ -92,6 +92,8 @@ Runtime: 36 ms, faster than 94.39% of C++ online submissions for Kth Smallest El
 
 Memory Usage: 11.1 MB, less than 100.00% of C++ online submissions for Kth Smallest Element in a Sorted Matrix.
 
+Guess a `mid` and then find out it's `count` th smallest number, we then decide to search left or right depending on the comparing result of `count` and `k`.
+
 ```cpp
 class Solution {
 public: