#include <iostream>

int main()
{
    unsigned long long f0, f1, n;
    std::cin >> f0 >> f1 >> n;
    
    if(n == 0)
    {
        std::cout << f0 << std::endl;
        return 0;
    }
    if(n == 1)
    {
        std::cout << f1 << std::endl;
        return 0;
    }
    
    unsigned long long next;
    for(unsigned long long i = 2; i <= n; i++)
    {
        next = f0 ^ f1;
        f0 = f1;
        f1 = next;
    }
    
    std::cout << next << std::endl;
    return 0;
}