#include<iostream>
#include<string>
#include<algorithm>
#include<cctype>
#include<set>
#include<bitset>
#include<math.h>
#include<map>
#include<queue>
#include<iomanip>
using namespace std;

int main(){
    long long f0, f1, n, f2;
    cin >> f0 >> f1 >> n;
    f2 = f0^f1;
    cout << (!(n%3) ? f0 : ((n%3 == 1) ? f1 : f2)) << endl;
}