#include<bits/stdc++.h>
#include<atcoder/all>
using namespace std;
using namespace atcoder;
#define rep(i,n)for (int i = 0; i < int(n); ++i)
#define rrep(i,n)for (int i = int(n)-1; i >= 0; --i)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
template<class T> void chmax(T& a, const T& b) {a = max(a, b);}
template<class T> void chmin(T& a, const T& b) {a = min(a, b);}
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

// returns (len_of_cycle, first_in-cycle_index)
template<class S, class F>
std::pair<int, int> detect_cycle(F f, S x) {
    S p = x, q = x;
    int l = 0;
    int ub = 1;
    do {
        if (l == ub) {
            ub <<= 1;
            l = 0;
            p = q;
        }
        q = f(q);
        l++;
    } while(p != q);
    p = q = x;
    for(int it = l; it > 0; it--) q = f(q);
    int m = 0;
    while(p != q) p = f(p), q = f(q), m++;
    return {l, m};
}

using S = tuple<int, int, int>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    auto f = [](S x) {
        auto [p, q, r] = x;
        return S{q, r, (p + q + r) % 10};
    };
    int p, q, r;
    ll k;
    cin >> p >> q >> r >> k;
    k -= 3;
    p %= 10, q %= 10, r %= 10;
    auto [l, m] = detect_cycle(f, S{p, q, r});
    if (k > m) {
        k = m + (k - m) % l;
    }
    S now{p, q, r};
    rep(_, k) {
        now = f(now);
    }
    cout << get<2>(now) << endl;
}