using System;

namespace No64_XORFibonacciSequence
{
    internal class Program
    {
        static void Main(string[] args) {
            string[] param = Console.ReadLine().Split(' ');
            long f0 = long.Parse(param[0]);
            long f1 = long.Parse(param[1]);
            long n = long.Parse(param[2]);

            long fk1 = f1;
            long fk2 = f0;
            for(long i = 2; i <= n; i++) {
                long fk = fk1 ^ fk2;
                fk2 = fk1;
                fk1 = fk;
            }
            Console.WriteLine(fk1);
        }
    }
}