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

int main() {
    int p[4];
    ll k;
    cin >> p[0] >> p[1] >> p[2] >> k;

    for (int i = 0; i < 3; i++) {
        p[i] %= 10;
    }

    int x[1000] = {}, y[2000];
    for (int l = 4; l < 2000; l++) {
        int s = 0, t = 0, u = 1;
        for (int i = 0; i < 3; i++) {
            s += p[i];
            t += p[i] * u;
            u *= 10;
        }
        p[3] = s % 10;
        if (l == k) {
            cout << p[3] << endl;
            exit(0);
        }
        if (x[t] != 0) {
            ll c = l - x[t];
            ll l0 = x[t] + (k - l) % c;
            cout << y[l0] << endl;
            exit(0);
        }
        x[t] = l;
        y[l] = p[3];
        for (int i = 0; i < 3; i++) {
            p[i] = p[i + 1];
        }
    }

    return 0;
}