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

namespace yukicode {
    public class Program {
        static UInt64 F0, F1, N;
        public static UInt64 FNumber(UInt64 n) {
            return n >= 2 ? (FNumber( n - 1 ) ^ FNumber( n - 2 )) : ( n == 1 ? F1 : F0 );
        }
        public static UInt64 Solver(System.IO.TextReader reader) {
            var buf = reader.ReadLine().Split();
            F0 = UInt64.Parse( buf[ 0 ] );
            F1 = UInt64.Parse( buf[ 1 ] );
            N = UInt64.Parse( buf[ 2 ] );
            return FNumber( N );
        }

        private static void Main() {
            Console.WriteLine( Solver( Console.In ) );
        }
    }
}