#include <iostream>

using namespace std;

int main(int argc, const char* argv[])
{
	uint64_t F0, F1, N;
	cin >> F0 >> F1 >> N;
	if (N == 1) {
		cout << F1 << endl;
		return 0;
	}
	for (uint64_t i = 2; i <= N; i++) {
		F0 = F1 ^ F0;
	}
	cout << F0 << endl;
	return 0;
}