diff --git "a/ksinji/202512/13 BOJ 4\354\231\200 7.md" "b/ksinji/202512/13 BOJ 4\354\231\200 7.md"
new file mode 100644
index 00000000..5b9790ee
--- /dev/null
+++ "b/ksinji/202512/13 BOJ 4\354\231\200 7.md"	
@@ -0,0 +1,38 @@
+```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));
+        long k = Long.parseLong(br.readLine());
+
+        long cnt = 2;
+        int len = 1;
+
+        while (k > cnt) {
+            k -= cnt;
+            cnt *= 2;
+            len++;
+        }
+
+        StringBuilder sb = new StringBuilder();
+
+        while (len > 0) {
+            long half = cnt / 2;
+
+            if (k <= half) {
+                sb.append('4');
+            } else {
+                sb.append('7');
+                k -= half;
+            }
+
+            cnt = half;
+            len--;
+        }
+
+        System.out.println(sb);
+    }
+}
+```