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

namespace yukicodeX {
	public class ProgramX {
		public static UInt64 Solver(System.IO.TextReader reader) {
			var buf = reader.ReadLine().Split();
			 UInt64[] f=new UInt64[3];
			f[0] = UInt64.Parse(buf[0]);
			 f[1] = UInt64.Parse(buf[1]);
			 f[2] = f[0] ^ f[1];
			var n = UInt64.Parse(buf[2]);
			return f[n%3];
		}
		
		private static void Main() {
			Console.WriteLine( Solver( Console.In ) );
		}
	}
}