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.*;
import java.lang.*;
import java.util.*;

public class Main
{
	static class FastReader 
	{ 
		BufferedReader br; 
		StringTokenizer st; 
  		
		public FastReader() 
		{ 
			br = new BufferedReader ( new InputStreamReader(System.in) ); 
		}
  
		String next() 
		{ 
			while (st == null || !st.hasMoreElements()) 
			{ 
				try
				{ 
					st = new StringTokenizer(br.readLine()); 
				} 
				catch (IOException  e) 
				{ 
					e.printStackTrace(); 
				} 
			} 
			return st.nextToken(); 
		} 
  
		int nextInt() 
		{ 
			return Integer.parseInt(next()); 
		} 
  
		long nextLong() 
		{ 
			return Long.parseLong(next()); 
		} 
  
		double nextDouble() 
		{ 
			return Double.parseDouble(next()); 
		} 
  
		String nextLine() 
		{ 
			String str = ""; 
			try
			{ 
				str = br.readLine(); 
			} 
			catch (IOException e) 
			{ 
				e.printStackTrace(); 
			} 
			return str; 
		} 
	} 
  
	public static void main(String args[])throws IOException
	{

		FastReader r = new FastReader();

		long N = r.nextLong();
		int digitsN = getDigits(N);

		if(digitsN%2==1)
		{
			StringBuilder ans = new StringBuilder();
			int temp = (digitsN/2)+1;
			for(int i = 0; i<temp; i++)
			{
				ans.append('4');
			}
			for(int i = 0; i<temp; i++)
			{
				ans.append('7');
			}
			System.out.println(ans.toString());
			return;
		}

		StringBuilder smallest = new StringBuilder();
		StringBuilder largest = new StringBuilder();
		int temp = (digitsN/2);
		for(int i = 0 ; i < temp; i++)
		{
			smallest.append('4');
			largest.append('7');
		}
		for(int i = 0 ; i < temp; i++)
		{
			largest.append('4');
			smallest.append('7');
		}

		if(  (Long.parseLong(largest.toString())>=N)  )
		{
			StringBuilder ans = new StringBuilder();
			ans = smallest;
			while(Long.parseLong(ans.toString()) < N)
			{
				int count_7 = 0;
				
				for(int i=2*temp-1; i>=0; i--)
				{
					if(ans.charAt(i)=='7')
					{
						count_7++;
						ans.setCharAt(i, '4');
					}
					else if(count_7>0)
					{
						ans.setCharAt(i, '7');
						break;
					}
				}

				for(int i = 0; i < count_7 - 1; i++)
				{
					ans.setCharAt(2*temp-1-i, '7');
				}

			}
			System.out.println(ans.toString());
			return;
		}
		else
		{
			StringBuilder ans = new StringBuilder();
			for(int i = 0 ; i < temp+1; i++)
			{
				ans.append('4');
			}
			for(int i = 0 ; i < temp+1; i++)
			{
				ans.append('7');
			}

			System.out.println(ans.toString());
			return;
		}

	}

	public static int getDigits(long N)
	{
		int count = 0;
		while(N>0)
		{
			count = count + 1;
			N = N/10;
		}
		return count;
	}
} 

class Node implements Comparable<Node>
{
	int index;
	int weight;
	ArrayList<Node> neighbours;

	public Node(int index, int weight)
	{
		this.index = index;
		this.weight = weight;
		this.neighbours = new ArrayList<>();
	}

	public int compareTo(Node y)
	{
		return -(this.weight - y.weight);
	}
}

class Graph
{
	int V;
	Node[] nodes;
	Graph(int V)
	{
		this.V = V;
		nodes = new Node[this.V];
	}

}