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.util.StringTokenizer;

public class Solution {

    public static void solve(InputReader in, PrintWriter out, DebugWriter debug) throws IOException {
        int n = in.nextInt();

        long min = 4444477777L;
        for (int len=0; len<=9; len++) {
            for (int i = 0; i < Math.pow(2, len); i++) {
                String bitmask = Integer.toBinaryString(i);
                while (bitmask.length() < len) bitmask = "0"+bitmask;

                int delta = 0;
                StringBuilder number = new StringBuilder();
                for (int j = 0; j < bitmask.length(); j++) {
                    if (bitmask.charAt(j) == '0') {
                        number.append('4');
                        delta++;
                    }
                    if (bitmask.charAt(j) == '1') {
                        number.append('7');
                        delta--;
                    }
                }

                long ans = Long.parseLong(number.toString());
                if (delta == 0 && ans < min && ans >= n) min = ans;
            }
        }

        out.print(min);
    }

    public static void main(String[] args) throws IOException{
        InputReader in;
        PrintWriter out;
        DebugWriter debug;

        if (args.length > 0 && args[0].equals("file")) {
            in = new InputReader(new BufferedReader(new FileReader("input.txt")));
            out = new PrintWriter(new FileWriter("output.txt"));
            debug = new DebugWriter(true);

            int sampleNumber = 1;
            do {
                String nextSample = "Sample #" + sampleNumber++ + ": ";
                out.println(nextSample);
                debug.println(nextSample);

                solve(in, out, debug);

                out.println("");
                debug.println("");
            } while (in.reader.readLine() != null);
        } else {
            in = new InputReader(new BufferedReader(new InputStreamReader(System.in)));
            out = new PrintWriter(new OutputStreamWriter(System.out));
            debug = new DebugWriter(false);

            solve(in, out, debug);
        }

        in.reader.close();
        out.close();
    }

    public static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(BufferedReader reader) {
            this.reader = reader;
            tokenizer = null;
        }

        public String next() throws IOException{
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                tokenizer = new StringTokenizer(reader.readLine());
            }

            return tokenizer.nextToken();
        }

        public int nextInt() throws IOException{
            return Integer.parseInt(next());
        }

        public int[] nextIntArray(int n) throws IOException{
            int[] array = new int[n];
            for (int i=0; i<n; i++){
                array[i] = nextInt();
            }

            return array;
        }
    }

    public static class DebugWriter {
        public boolean enable;

        public DebugWriter(boolean enable){
            this.enable = enable;
        }

        public void print(Object o){
            if (enable) System.out.print(o);
        }

        public void println(Object o){
            if (enable) System.out.println(o);
        }
    }

}