#include <iostream>
using namespace std;

long long p, q, r, K;
long long A[1 << 24];

int main() {
	// Step #1. Input
	cin >> p >> q >> r >> K;
	A[1] = p % 10LL;
	A[2] = q % 10LL;
	A[3] = r % 10LL;

	// Step #2. Solve
	for (long long i = 4; i <= K; i++) A[i] = (A[i - 1] + A[i - 2] + A[i - 3]) % 10LL;
	cout << A[K] << endl;
	return 0;
}