#include <iostream>
#include <vector>
#include <bits/stdc++.h>
int main() {
	unsigned long long f0,f1,n;
	std::cin>>f0>>f1>>n;
	std::vector<unsigned long long> fib;
	fib.resize(n+1);
	fib[0]=f0;
	if(n>0){
		fib[1]=f1;
	}
	for(int i=2;i<n+1;i++){
		fib[i]=fib[i-1]^fib[i-2];
	}
	std::cout<<fib[n]<<std::endl;
	return 0;
}