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.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.StringTokenizer;

public class B {
	private static BufferedReader in;
	private static StringTokenizer st;
	private static PrintWriter out;
	
	public static void main(String[] args) throws IOException {
		in = new BufferedReader(new InputStreamReader(System.in));
		st = new StringTokenizer("");
		out = new PrintWriter(new BufferedWriter(new OutputStreamWriter(System.out)));
		int n = nextInt();
		int pow = (1<<10);
		int a[] = new int [10];
		long ans = Long.MAX_VALUE;
		for (int i = 0; i < pow; i++) {
			Arrays.fill(a, 0);
			int t = i;
			int cnt = 0;
			int cnt2 = 0;
			while(t > 0){
				a[cnt++] = t % 2;
				cnt2 += a[cnt-1];
				t/=2;
			}
			long m1 = 0;
			long m2 = 0;
			for (int j = 0; j < cnt; j++) {
				if(a[j]==0){
					m1 = m1 * 10 + 4; 
					m2 = m2 * 10 + 7; 
				}else{
					m1 = m1 * 10 + 7; 
					m2 = m2 * 10 + 4;
				}
			}
			if(cnt2 == cnt - cnt2){
				if(m1 >=n){
					ans = Math.min(ans, m1);
				}
				if(m2 >=n){
					ans = Math.min(ans, m2);
				}
			}
		}
		System.out.println(ans);
	}
	static String next() throws IOException{
		while(!st.hasMoreTokens()){
			st = new StringTokenizer(in.readLine());
		}
		return st.nextToken();
	}
	static int nextInt() throws NumberFormatException, IOException{
		return Integer.parseInt(next());
	}
	static long nextLong() throws NumberFormatException, IOException{
		return Long.parseLong(next());
	}
	
	static double nextDouble() throws NumberFormatException, IOException{
		return Double.parseDouble(next());
	}

}