#include <stdio.h>

int main() {
	long long int f0, f1, n, f, i;

	scanf("%lld %lld %lld", &f0, &f1, &n);

	if (n == 0) f = f0;
	else if (n == 1) f = f1;
	else {
		for (i = 0; i < n - 1; i++) {
			f = f0 ^ f1;
			f0 = f1;
			f1 = f;
		}
	}

	printf("%lld\n", f);

	return 0;
}