#include <iostream>
#include <vector>

int32_t main() {
    uint64_t f0, f1, n;
    std::cin >> f0 >> f1 >> n;

    std::vector<uint64_t> fibs{f0, f1};
    for (uint64_t i = 2; i <= n; ++i) {
        fibs.push_back(fibs.at(i - 1) ^ fibs.at(i - 2));
    }

    std::cout << fibs.at(n) << std::endl;
}