#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>

using namespace std;

int main() {
	int n, k;
	string s;

	cin >> n >> k >> s;

	int more = 0;
	for (int i = 0; i < n; i++) {
		more += s[i] - '0';
	}
	int buy_per_box = n - more;
	if (buy_per_box < 0) {
		buy_per_box = 0;
	}

	int n_full = k / n;

	int limit = k % n + (n_full > 0) * n;
	int ans = 0;
	int hit = 0;
	for (int i = 0; i < limit; i++) {
		if (hit > 0) {
			hit--;
		} else {
			ans++;
		}
		hit += s[i % n] - '0';
	}
	if (n_full > 0) {
		ans += buy_per_box * (n_full - 1);
	}
	cout << ans << endl;
	return 0;
}