#include <bits/stdc++.h>
using namespace std;
#define repd(i,a,b) for (int i=(a);i<(b);i++)
#define rep(i,n) repd(i,0,n)
#define all(x) (x).begin(),(x).end()
#define SIZE(x) ll(x.size())
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return true; } return false; }
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return true; } return false; }
typedef long long ll;
const long long INF = 1LL << 60;
const long long MOD = 1000000007;
typedef pair<int, int> P;
typedef tuple<int, int, int> T;
int main()
{
    ll p, q, r, K;
    cin >> p >> q >> r >> K;

    p %= 10; q %= 10; r %= 10;
    K -= 3;

    map<T, int> mp;
    map<int, int> revmp;
    mp[{p, q, r}] = 0;
    revmp[0] = r;
    int cnt = 1;

    while (1) {
        int tr = r, tq = q;
        r = (p + q + r) % 10;
        q = tr;
        p = tq;
        if (mp.count({p, q, r}) > 0) break;
        mp[{p, q, r}] = cnt;
        revmp[cnt] = r;
        K--;
        cnt++;
        if (K == 0) {
            cout << r << endl;
            return 0;
        }
    }

    K %= cnt;
    K--;
    if (K < 0) K += cnt;

    cout << revmp[K] << endl;
    return 0;
}