//#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
//using namespace atcoder;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<ll>>;
Graph G;
vll dist;
vector<bool> seen;

ll mod = 10;

vector<vector<vector<ll>>> matrixpow;
void prematrixpow(vector<vll> matrix) {
	ll N = matrix.size();
	matrixpow.assign(70, vector<vll>(N, vll(N)));
	rep(h, N) {
		rep(w, N) {
			matrixpow[0][h][w] = matrix[h][w];
		}
	}
	rep(k, 69) {
		rep(h, N) {
			rep(w, N) {
				ll S = 0;
				rep(i, N) {
					S += matrixpow[k][h][i] * matrixpow[k][i][w];
					S %= mod;
				}
				matrixpow[k + 1][h][w] = S;
			}
		}
	}

}
vector<vll> modmatrixpow(ll K) {
	ll P = K;
	ll N = matrixpow[0].size();
	vector<vll> res(N, vll(N, 0));
	rep(i, N) {
		res[i][i] = 1;
	}

	rep(j, 70) {
		if (P % 2 != 0) {
			vector<vll> res2(N, vll(N, 0));

			rep(h, N) {
				rep(w, N) {
					ll S = 0;
					rep(i, N) {
						S += matrixpow[j][h][i] * res[i][w];
						S %= mod;
					}
					res2[h][w] = S;
				}
			}
			res = res2;
		}
		P /= 2;
	}

	return res;


}
int main() {
    ll P,Q,R,K;
    cin>>P>>Q>>R>>K;
    vector<vll> D={{1,1,1,0},{1,0,0,0},{0,1,0,0},{0,0,1,0}};
    prematrixpow(D);
    auto AN=modmatrixpow(K-3);
    ll n=AN[0][0]*R+AN[0][1]*Q+AN[0][2]*P;
    cout<<n%10<<endl;

}