#include <iostream>
#include <vector>
using namespace std;

int main() {
  unsigned long long f0, f1, n;
  cin >> f0 >> f1 >> n;
  vector<unsigned long long> v;
  v.push_back(f0);
  v.push_back(f1);
  for (int i = 2; i < n + 1; i++) {
    unsigned long long tmp = v[i - 1] ^ v[i - 2];
    v.push_back(tmp);
  }
  cout << v[n] << endl;
  return 0;
}