#include<bits/stdc++.h>
using namespace std;
using ll = long long int;
using ld = long double;
const ll MAX = 5000000000000000000;
const ld PI = 3.14159265358979;
const ll MOD = 0;//2024948111;
random_device rd;
mt19937 mt(rd());
ld dotorad(ld K){return PI * K / 180.0;}
ld radtodo(ld K){return K * 180.0 / PI;}
int main(){
    ll p,q,r,K;
    cin >> p >> q >> r >> K;
    p %= 10;
    q %= 10;
    r %= 10;
    K -= 3;
    vector<ll> memo(1000,-1);
    ll c = 0;
    while(1){
        ll h = p * 100 + q * 10 + r;
        if(memo[h] != -1) break;
        memo[h] = c;
        ll x = p;
        p = q;
        q = r;
        r = (p + q + x) % 10;
        c++;
    }
    ll h = p * 100 + q * 10 + r;
    ll d = c - memo[h];
    if(K >= memo[h]){
        K = (K - memo[h]) % d + memo[h];
    }
    for(ll i = 0;i < 1000;i++) if(memo[i] == K) cout << i % 10 << endl;
}