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

namespace Test
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] a = Console.ReadLine().Split();
            string[] b = Console.ReadLine().Split();
            if (a[1] == b[1]) Console.WriteLine(-1);
            else if (a[1].Length != b[1].Length)
            {
                Console.WriteLine(a[1].Length > b[1].Length ? a[0] : b[0]);
            }
            else
            {
                bool flag = true;
                for (int i = 0; flag; i++)
                {
                    if (a[1][i] != b[1][i])
                    {
                        flag = false;
                        Console.WriteLine(a[1][i] > b[1][i] ? a[0] : b[0]);
                    }
                }
            }
        }
    }
}