import java.util.Scanner;

public class Yukicoder64 {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long f0 = sc.nextLong();
		long f1 = sc.nextLong();
		long N = sc.nextLong();
		
		long fn = 0;
		
		if (N == 0) fn = f0;
		else if (N == 1) fn = f1;
		else {
			for (long i = 2; i <= N; i++) {
				fn = f0 ^ f1;
				f0 = f1;
				f1 = fn;
			}
		}
		System.out.println(fn);
	}
}