#include <iostream>
#include <vector>
#include <algorithm>
#include <cmath>
#include <iomanip>
#include <stack>
#include <algorithm>
#include <string>
#include <map>
#include <iterator>
#include <set>
#include <queue>
#include <bitset>
#include <cassert>

using namespace std;

int main() {

    unsigned long long F0, F1, N;
    cin >> F0 >> F1 >> N;


    if (N == 0) {
        cout << F0 << endl;
    } else if (N == 1) {
        cout << F1 << endl;
    } else {
        unsigned long long Fi;
        for (int i = 1; i < N; ++i) {
            Fi = F1 ^ F0;
            unsigned long long tmp = F1;
            F1 = Fi;
            F0 = tmp;
        }
        cout << Fi << endl;
    }


}