#include <bits/stdc++.h> 

using namespace std;
typedef long long ll;

int main() {
    ll F0, F1, N;
    cin >> F0 >> F1 >> N;
    vector<ll> v(N+1, 0);
    v[0] = F0;
    v[1] = F1;
    for (int i = 2; i <= N; i++) {
        v[i] = v[i - 2] ^ v[i - 1];
    }
    cout << v[N] << endl;
}