diff --git "a/khj20006/202508/28 BOJ P4 \354\213\234\352\260\204\354\235\200 \353\213\244\354\213\234 \354\233\200\354\247\201\354\235\270\353\213\244.md" "b/khj20006/202508/28 BOJ P4 \354\213\234\352\260\204\354\235\200 \353\213\244\354\213\234 \354\233\200\354\247\201\354\235\270\353\213\244.md"
new file mode 100644
index 00000000..5656384b
--- /dev/null
+++ "b/khj20006/202508/28 BOJ P4 \354\213\234\352\260\204\354\235\200 \353\213\244\354\213\234 \354\233\200\354\247\201\354\235\270\353\213\244.md"	
@@ -0,0 +1,90 @@
+```java
+import java.util.*;
+import java.io.*;
+
+class IOController {
+	BufferedReader br;
+	BufferedWriter bw;
+	StringTokenizer st;
+
+	public IOController() {
+		br = new BufferedReader(new InputStreamReader(System.in));
+		bw = new BufferedWriter(new OutputStreamWriter(System.out));
+		st = new StringTokenizer("");
+	}
+
+	String nextLine() throws Exception {
+		String line = br.readLine();
+		st = new StringTokenizer(line);
+		return line;
+	}
+
+	String nextToken() throws Exception {
+		while (!st.hasMoreTokens()) nextLine();
+		return st.nextToken();
+	}
+
+	int nextInt() throws Exception {
+		return Integer.parseInt(nextToken());
+	}
+
+	long nextLong() throws Exception {
+		return Long.parseLong(nextToken());
+	}
+
+	double nextDouble() throws Exception {
+		return Double.parseDouble(nextToken());
+	}
+
+	void close() throws Exception {
+		bw.flush();
+		bw.close();
+	}
+
+	void write(String content) throws Exception {
+		bw.write(content);
+	}
+
+}
+
+public class Main {
+
+	static IOController io;
+
+	//
+
+	static int N;
+	static int[] a;
+	static boolean[][] dp;
+
+	public static void main(String[] args) throws Exception {
+
+		io = new IOController();
+
+		N = io.nextInt();
+		a = new int[200001];
+		for(int i=0;i<N;i++) a[io.nextInt()]++;
+		for(int i=1;i<=200000;i++) a[i] += a[i-1];
+		dp = new boolean[200001][450];
+
+		for(int i=0;i<=200000;i++) {
+			if(a[i] > 1) dp[i][1] = false;
+			else dp[i][1] = true;
+		}
+		for(int t=2;t<450;t++) for(int i=(t-1)*t+t-1;i<=200000;i++) {
+			if(a[i] - a[i-1] == 0) dp[i][t] = dp[i-1][t];
+			if(dp[i-2*t+1][t-1] && (a[i-t]-a[i-2*t+1] == 0)) dp[i][t] = true;
+		}
+		for(int t=1;t<450;t++) if(dp[200000][t]) {
+			io.write("YES");
+			io.close();
+			return;
+		}
+		io.write("NO");
+
+		io.close();
+
+	}
+
+}
+```