Problem: Petya loves lucky numbers. Everybody knows that positive integers are lucky if their decimal representation doesn't contain digits other than 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.

Lucky number is super lucky if it's decimal representation contains equal amount of digits 4 and 7. For example, numbers 47, 7744, 474477 are super lucky and 4, 744, 467 are not.

One day Petya came across a positive integer n. Help him to find the least super lucky number which is not less than n.

Input

The only line contains a positive integer n (1 ≤ n ≤ 10100000). This number doesn't have leading zeroes.

Output

Output the least super lucky number that is more than or equal to n.

Examples

Input

4500


Output

4747


Input

47


Output

47

Solution (in JAVA):

Solution:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.StringTokenizer;


public class ProblemB1 implements Runnable {
	long result = 4444477777L;
	int n;
	private void solve() throws IOException {
		n = nextInt();
		dfs(7, 0, 1);
		dfs(4, 1, 0);
		writer.println(result);
	}
	private void dfs(long x, int four, int seven) {
		if (x > 4444477777L) {
			return;
		}
		if (four == seven && x < result && x >= n) {
			result = x;
		}
		dfs(x * 10 + 4, four + 1, seven);
		dfs(x * 10 + 7, four, seven + 1);
	}
	StringTokenizer tokenizer;
	BufferedReader reader;
	PrintWriter writer;
	
	@Override
	public void run() {
		try {
			tokenizer = null;
			reader = new BufferedReader(new InputStreamReader(System.in));
			writer = new PrintWriter(System.out);
			solve();
			reader.close();
			writer.close();
		} catch (Exception e) {
			e.printStackTrace();
			System.exit(1);
		}
	}
	
	private String nextToken() throws IOException {
		while (tokenizer == null || !tokenizer.hasMoreTokens()) {
			tokenizer = new StringTokenizer(reader.readLine());
		}
		return tokenizer.nextToken();
	}
	
	private int nextInt() throws IOException {
		return Integer.parseInt(nextToken());
	}
	
	private long nextLong() throws IOException {
		return Long.parseLong(nextToken());
	}
	
	private double nextDouble() throws IOException {
		return Double.parseDouble(nextToken());
	}
	
	public static void main(String[] args) {
		new ProblemB1().run();
	}
	

}