diff --git "a/ksinji/202511/21 BOJ \353\271\227\353\254\274.md" "b/ksinji/202511/21 BOJ \353\271\227\353\254\274.md"
new file mode 100644
index 00000000..0bb8fc07
--- /dev/null
+++ "b/ksinji/202511/21 BOJ \353\271\227\353\254\274.md"	
@@ -0,0 +1,35 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        int h = Integer.parseInt(st.nextToken());
+        int w = Integer.parseInt(st.nextToken());
+
+        int[] height = new int[w];
+
+        st = new StringTokenizer(br.readLine());
+        for (int i=0; i<w; i++){
+            height[i] = Integer.parseInt(st.nextToken());
+        }
+
+        int answer=0, l=0;
+
+        for (int i=1; i<w-1; i++){
+            l = Math.max(l, height[i-1]);
+            int r = 0;
+            for (int j=i+1; j<w; j++){
+                r = Math.max(r, height[j]);
+            }
+
+            if (height[i] < l && height[i] < r) answer+=Math.min(l, r)-height[i];
+        }
+
+        System.out.println(answer);
+    }
+}
+```