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.IOException;
import java.util.*;
import java.util.Arrays;
import java.util.Scanner;

public class Bit_year{
	static Set<String> set;
	public static void main(String[] args) throws IOException {
		
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		set = new TreeSet<String>();
		
		System.out.println((long)permute(n));
		
	}
	public static long permute(int n){
		
		int pow=2;
		while(pow<=10)
		{
			char[] ar = new char[pow];
			//System.out.println("lenght"+pow);
			for(int i=0;i<pow/2;i++)ar[i]='4';
			for(int i=pow/2;i<pow;i++)ar[i]='7';
			permuteHelper(ar, 0);
			//System.out.println(set.toString());
			for(String s : set)
			{
				if(Long.parseLong(s)>=n) {return Long.parseLong(s);}
			}
			
			pow+=2;
		}
		return 0;
	}
	private static void permuteHelper(char[] arr, int index){
	    if(index >= arr.length - 1){ //If we are at the last element - nothing left to permute
	    	set.add(new String(arr));
	        //System.out.println(Arrays.toString(arr));
	        return;
	    }

	    for(int i = index; i < arr.length; i++){ //For each index in the sub array arr[index...end]

	        //Swap the elements at indices index and i
	        char t = arr[index];
	        arr[index] = arr[i];
	        arr[i] = t;

	        //Recurse on the sub array arr[index+1...end]
	        permuteHelper(arr, index+1);

	        //Swap the elements back
	        t = arr[index];
	        arr[index] = arr[i];
	        arr[i] = t;
	    }
	}
	
}