#include <bits/stdc++.h>

using namespace std;

int seen[10][10][10];

int main(){
    int64_t p, q, r, k;
    cin >> p >> q >> r >> k;
    p %= 10;
    q %= 10;
    r %= 10;
    for(int i = 0;i < 10;i++){
        for(int j = 0;j < 10;j++){
            for(int l = 0;l < 10;l++) seen[i][j][l] = -1;
        }
    }
    seen[p][q][r] = 3;
    bool looped = false;
    for(int i = 4;i <= k;i++){
        int np = q;
        int nq = r;
        int nr = (p + q + r) % 10;
        p = np;
        q = nq;
        r = nr;
        if(seen[p][q][r] == -1 || looped){
            seen[p][q][r] = i;
        }
        else{
            int loop = i - seen[p][q][r];
            looped = true;
            k %= loop;
            while(k < i) k += loop;
        }
    }
    cout << r << endl;
}