package me.yukicoder;

import java.util.Scanner;

/**
 * No.293 4>7の世界
 * star 2
 * http://yukicoder.me/problems/728
 */
public class YukiCoder293 {

    public static void main(String[] args) {
        run();
    }

    public static void run() {
        Scanner sc = new Scanner("1237564890 1234567890");
//        Scanner sc = new Scanner(System.in);
        String s = sc.nextLine();
        String[] org = s.split(" ");
        String l = org[0];
        String r = org[1];
        s = s.replace('4', 'A');
        s = s.replace('7', '4');
        s = s.replace('A', '7');
        String[] ss = s.split(" ");
        long a = Long.parseLong(ss[0]);
        long b = Long.parseLong(ss[1]);
        boolean left = false;
        if (a > b) {
            left = true;
        }

        System.out.println(left ? l : r);
//        System.out.println(Math.max(a, b));
    }
/*
4 7
4

5 7
5

40 170
170

1237564890 1234567890
1234567890
 */

}