//No.64 XORフィボナッチ数列
#include <iostream>
#include <vector>
using namespace std;

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