#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define srep(i, s, t) for (int i = s; i < t; ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
#define MAX_N 200005

int main() {
    ll p, q, r, K;
    cin >> p >> q >> r >> K;
    p %= 10;
    q %= 10;
    r %= 10;
    ll a[10][10][10];
    rep(i, 10) rep(j, 10) rep(k, 10) a[i][j][k] = 0;
    a[p][q][r]                                  = 3;
    ll now                                      = 3;
    ll loop                                     = 0;
    while (now < K) {
        int next = (p + q + r) % 10;
        now++;
        // cout << now << ' ' << q << ' ' << r << ' ' << next << endl;
        if (a[q][r][next] != 0) {
            loop = now - a[q][r][next];
            now += (K - now) / loop * loop;
            p = q;
            q = r;
            r = next;
            break;
        } else {
            a[q][r][next] = now;
            p             = q;
            q             = r;
            r             = next;
        }
    }
    while (now < K) {
        int next = (p + q + r) % 10;
        now++;
        // cout << now << ' ' << q << ' ' << r << ' ' << next << endl;
        a[q][r][next] = now;
        p             = q;
        q             = r;
        r             = next;
    }
    if (now == K) {
        cout << r << endl;
        return 0;
    }
    return 0;
}