#include <bits/stdc++.h>

int main() {
    unsigned long f0, f1, n;
    std::cin >> f0 >> f1 >> n;
    if (n == 0) {
        std::cout << f0 << std::endl;
    } else if (n == 1) {
        std::cout << f1 << std::endl;
    } else {
        unsigned long fi, fi_1, fi_2;
        fi_1 = f1;
        fi_2 = f0;
        for (unsigned long i = 2; i <= n; i++) {
            fi = fi_1 ^ fi_2;
            fi_2 = fi_1;
            fi_1 = fi;
        }
        std::cout << fi << std::endl;
    }

    return 0;
}