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.lang.*;
import java.math.*;
import java.util.*;
import java.io.*;

public class Main {

    void solve() {
        s=ns().toCharArray();
        int n=s.length;
        int b=1;
        int cnt=0;
        for(int i=0;i<n;i++){
            if(s[i]-'0'<7) {
                b = 0;
            }else if(s[i]-'0'>7) {
               break;
            }
        }
        if(n%2==1){
            int l=n+1;
            for(int i=1;i<=l/2;i++) pw.print("4");
            for(int i=1;i<=l/2;i++) pw.print("7");
            return;
        }else
        if(b==1){

            int l=n;
            if(n%2==0) l+=2;

            for(int i=1;i<=l/2;i++) pw.print("4");
            for(int i=1;i<=l/2;i++) pw.print("7");

            return;
        }


        go(0,0,true,n);
        if(!check) {
            int l=n+2;
            for(int i=1;i<=l/2;i++) pw.print("4");
            for(int i=1;i<=l/2;i++) pw.print("7");
        }


    }
    char s[];
    Stack<Integer> stk=new Stack<>();
    boolean check=false;
    void go(int i,int diff,boolean equal,int n){

        if(i>=n){
            if(diff==0){
                for(int u : stk)System.out.print(u);
                check=true;
                System.exit(0);
            }
            return;
        }
        if(Math.abs(diff)>n-i) return;
        if(equal){
            if(s[i]-'0'<4){
                stk.push(4);
                go(i+1,diff+1,false,n);
                stk.pop();
                stk.push(7);
                go(i+1,diff-1,false,n);
                stk.pop();
            }else if(s[i]-'0'==4){
                stk.push(4);
                go(i+1,diff+1,true,n);
                stk.pop();
                stk.push(7);
                go(i+1,diff-1,false,n);
                stk.pop();
            }else if(s[i]-'0'<7){
                stk.push(7);
                go(i+1,diff-1,false,n);
                stk.pop();
            }else if(s[i]-'0'==7){

                stk.push(7);
                go(i+1,diff-1,true,n);
                stk.pop();
            }else {

            }
        }else {
            stk.push(4);
            go(i+1,diff+1,false,n);
            stk.pop();
            stk.push(7);
            go(i+1,diff-1,false,n);
            stk.pop();
        }



    }


    long M= (long)1e9+7;
    InputStream is;
    PrintWriter pw;
    String INPUT = "";
    void run() throws Exception {
        is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
        pw = new PrintWriter(System.out);
        long s = System.currentTimeMillis();
        solve();
        pw.flush();
        if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");

    }
    public static void main(String[] args) throws Exception { new Main().run(); }

    private byte[] inbuf = new byte[1024];
    public int lenbuf = 0, ptrbuf = 0;

    private int readByte() {
        if(lenbuf == -1)throw new InputMismatchException();
        if(ptrbuf >= lenbuf){
            ptrbuf = 0;
            try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
            if(lenbuf <= 0)return -1;
        }
        return inbuf[ptrbuf++];
    }

    private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
    private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }

    private double nd() { return Double.parseDouble(ns()); }
    private char nc() { return (char)skip(); }

    private String ns() {
        int b = skip();
        StringBuilder sb = new StringBuilder();
        while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ')
            sb.appendCodePoint(b);
            b = readByte();
        }
        return sb.toString();
    }

    private char[] ns(int n) {
        char[] buf = new char[n];
        int b = skip(), p = 0;
        while(p < n && !(isSpaceChar(b))){
            buf[p++] = (char)b;
            b = readByte();
        }
        return n == p ? buf : Arrays.copyOf(buf, p);
    }

    private char[][] nm(int n, int m) {
        char[][] map = new char[n][];
        for(int i = 0;i < n;i++)map[i] = ns(m);
        return map;
    }

    private int[] na(int n) {
        int[] a = new int[n];
        for(int i = 0;i < n;i++)a[i] = ni();
        return a;
    }

    private int ni() {
        int num = 0, b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-'){
            minus = true;
            b = readByte();
        }

        while(true){
            if(b >= '0' && b <= '9'){
                num = num * 10 + (b - '0');
            }else{
                return minus ? -num : num;
            }
            b = readByte();
        }
    }

    private long nl() {
        long num = 0;
        int b;
        boolean minus = false;
        while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
        if(b == '-'){
            minus = true;
            b = readByte();
        }

        while(true){
            if(b >= '0' && b <= '9'){
                num = num * 10 + (b - '0');
            }else{
                return minus ? -num : num;
            }
            b = readByte();
        }
    }
    private boolean oj = System.getProperty("ONLINE_JUDGE") != null;
    private void tr(Object... o) { if(INPUT.length() > 0)System.out.println(Arrays.deepToString(o)); }

}