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

namespace OddTimes
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            int[] numbers = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int result = numbers[0];

            for (int i = 1; i < numbers.Length; i++)
            {
                result = result ^ numbers[i];
            }

            Console.WriteLine(result);

            //example with first input:result=numbers[0]=1=001; result=010^001=011; result=011^011=000; 010^000=010; 011^010=001; 001^001=000; result=011^000=011=3;

        }
    }
}