#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;
using ld = long double;

template <typename T>
inline bool chmax(T &a, const T &b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

template <typename T>
inline bool chmin(T &a, const T &b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

// #include <atcoder>
// using namespace atcoder;
// using mint = modint1000000007;
// using mint = modint998244353;

// const int MOD = 1000000007;
// const int MOD = 998244353;

int main() {
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);
    int p, q, r;
    ll K;
    cin >> p >> q >> r >> K;
    vector<int> v(2000, 0);
    v[0] = p % 10;
    v[1] = q % 10;
    v[2] = r % 10;
    for (int i = 3; i < 2000; i++) {
        v[i] = (v[i - 1] + v[i - 2] + v[i - 3]) % 10;
    }
    ll x, y;
    bool fg = 0;
    for (int i = 3; i < 2000; i++) {
        for (int j = i + 1; j < 2000; j++) {
            if (v[i - 1] == v[j - 1] && v[i - 2] == v[j - 2] && v[i - 3] == v[j - 3]) {
                x = i;
                y = j - i;
                fg = 1;
                break;
            }
        }
        if (fg) {
            break;
        }
    }
    cout << v[x + (K - x + 1) % y - 2] << endl;
    return 0;
}