#include <iostream>
#include <cassert>
using namespace std;

long long p, q, r, K;
long long A[1 << 18];
long long used[1009];

int main() {
	// Step #1. Input
	cin >> p >> q >> r >> K;
	assert(1LL <= p && p <= 1000000000LL);
	assert(1LL <= q && q <= 1000000000LL);
	assert(1LL <= r && r <= 1000000000LL);
	assert(4LL <= K && K <= 1000000000000000000LL);
	A[1] = p % 10LL;
	A[2] = q % 10LL;
	A[3] = r % 10LL;
	used[A[1] * 1 + A[2] * 10 + A[3] * 100] = 3;

	// Step #2. Solve
	long long res = K;
	for (long long i = 4; i <= K; i++) {
		A[i] = (A[i - 1] + A[i - 2] + A[i - 3]) % 10LL;
		long long nex = A[i - 2] * 1 + A[i - 1] * 10 + A[i] * 100;
		if (used[nex] != 0LL) {
			long long cycle = i - used[nex];
			res = (K - used[nex]) % cycle + used[nex];
			break;
		}
		used[nex] = i;
	}

	// Step #3. Output
	cout << A[res] << endl;
	return 0;
}