#include <bits/stdc++.h>
using namespace std;
int main(){
    long long p,q,r;
    cin >> p >> q >> r;
    long long K;
    cin >> K;
    vector<tuple<int, int, int>> v;
    v.push_back({r % 10, q % 10, p % 10});
    set<tuple<int, int, int>> se;
    int now = 0;
    while(true){
        auto [s, t, u] = v[now];
        tuple<int, int, int> P = {(s + t + u) % 10 ,s, t};
        v.push_back(P);
        now++;
        if(se.count(P)) break;
        se.insert(P);
    }
    if(K < 3 + (long long)v.size()){
        auto [a, b, c] = v[K - 3];
        cout << a << endl;
        return 0;
    }
    int ind = -1;
    for(int i = 0; i < v.size(); i++){
        if(v[i] == v[now]) {
            ind = i;
            break;
        }
    }
    int sz = now - ind;
    K -= ind + 3;
    K %= sz;
    auto [s, t, u] = v[ind + K];
    cout << s << endl;
}