using System;

public class Hello
{
    public static void Main()
    {
        string[] line = Console.ReadLine().Trim().Split(' ');
        var a = line[0];
        var b = line[1];
        Console.WriteLine(getAns(a, b));
    }
    public static string getAns(string a, string b)
    {
        if (a.Length > b.Length) return a;
        else if (a.Length < b.Length) return b;
        for (int i = 0; i < a.Length; i++)
        {
            var a2 = int.Parse(a[i].ToString());
            var b2 = int.Parse(b[i].ToString());
            if (a2 == 4 && b2 == 7) return a;
            else if (a2 == 7 && b2 == 4) return b;
            else if (a2 > b2) return a;
            else if (a2 < b2) return b;
        }
        return "";
    }
}