#include <iostream>

auto main() -> int {
	long F0, F1, N;
	std::cin >> F0 >> F1 >> N;

	long FN;
	switch (N) {
	case 0:
		FN = F0;
		break;
	case 1:
		FN = F1;
		break;
	default:
		int a=0, b=F0, c=F1;
		for (int i = 1; i < N; i++) {
			a = b;
			b = c;
			c = a ^ b;
		}
		FN = c;
		break;
	}

	std::cout << FN << std::endl;
}