#include<iostream>
#include<vector>
using namespace std;
int main() {
    long long p, q, r, k; cin >> p >> q >> r >> k;
    long one, two, three;
    one = p % 10;
    two = q % 10;
    three = r % 10;
    for (long long i = 3; i < k; i++) {
        long tmp = three;
        three = (one + two + three) % 10;
        one = two;
        two = tmp;
    }
    cout << three << endl;
    return 0;
}