#include <iostream>
using namespace std;

int main(){
  long long int f0,f1,n,fn;
  int i;

  cin >> f0 >> f1 >> n;

  for(i=0;i<=n-2;++i){
    fn=f0^f1;
    f0=f1;
    f1=fn;
  }
  
  cout << fn << endl;

  return 0;
}