// yuki 1595 The Final Digit
// 2021.8.11

#include <stdio.h>

typedef long long ll;
int a[1000];

int main() {
	int p, q, r, s, t, f;
	ll K;
	scanf("%d%d%d%lld", &p, &q, &r, &K);
	p %= 10, t = p;
	q %= 10, t = t*10 + q;
	r %= 10, t = t*10 + r;
	K -= 3, f = 1;
	while (K) {
		if (f && a[t]) {
			K %= (a[t] - (int)K);
			f = 0;
		}
		a[t] = (int)K;
		s = (p+q+r) % 10;
		p = q, q = r, r = s;
		t = (t*10 + s) % 1000;
		K--;
	}
	printf("%d\n", s);
	return 0;
}