import java.util.*;
public class Fib{
	public static void main(String[] arg){
		Scanner sc = new Scanner(System.in);
		long f0,f1,f2,n;
		f0 = sc.nextLong();
		f1 = sc.nextLong();
		n = sc.nextLong();
		f2 = f0^f1;
		if(n%3 == 0){
			System.out.println(f0);
		}else if (n%3 ==1){
			System.out.println(f1);
		}else{
			System.out.println(f2);
		}
	}
}