using System;
using System.Collections.Generic;
using System.Linq;

class Program {
    static int ReadInt() { return int.Parse(Console.ReadLine()); }
    static int[] ReadInts() { return Console.ReadLine().Split().Select(int.Parse).ToArray(); }
    static string[] ReadStrings() { return Console.ReadLine().Split(); }

    static void Calc(string a, string b) {
        if (a.Length == b.Length) {
            for (int i = 0; i < a.Length; i++) {
                int x = a[i] - '0';
                int y = b[i] - '0';
                if (x == 4 && y == 7) {
                    Console.WriteLine(a);
                    return;
                }
                else if (x == 7 && y == 4) {
                    Console.WriteLine(b);
                    return;
                }
                else if (x != y) {
                    Console.WriteLine(x < y ? b : a);
                    return;
                }
            }
            // a == b
            Console.WriteLine(a);
        }
        else {
            var x = new[] { a, b }.OrderBy(e => e.Length).Last();
            Console.WriteLine(x);
        }
    }

    static void Main() {
        var ab = ReadStrings();
        Calc(ab[0], ab[1]);
    }
}