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

namespace YukiCoder
{
    class Program
    {
        static void Main(string[] args)
        {
            var va = Console.ReadLine().Split().ToArray();
            var vb = Console.ReadLine().Split().ToArray();
            var nn = ACmpB(va[1], vb[1]);
            var SS = nn > 0 ? va[0] : nn < 0 ? vb[0] : "-1";
            Console.WriteLine(SS);
            Console.ReadLine();
        }
        //- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - //
        static int ACmpB(string SA, string SB)
        {
            int nL = SA.Length - SB.Length;
            if (nL>0) return +1;
            if (nL<0) return -1;
            for (int i = 0; i < SA.Length; i++)
            {
                if (SA[i] > SB[i]) return +1;
                if (SA[i] < SB[i]) return -1;
            }
            return 0;
        }
    }
}