#include <bits/stdc++.h>
using namespace std;

int main(void) {
	int N, K;
	cin >> N >> K;
	string S;
	cin >> S;
	
	int now = 0;
	vector<int> A(N + 1, 0);
	for(int i = 0; i < N; ++i) {
		A[i + 1] = A[i];
		if(now == 0) {
			A[i + 1] += 1;
			now += 1;
		}
		now -= 1;
		now += (S[i] - '0');
	}
	
	if(K <= N) {
		cout << A[K] << "\n";
		return 0;
	}
	
	int ans = A[N];
	K -= N;
	for(int i = 0; i <= N; ++i) A[i] = max(0, A[i] - now);
	
	ans += (K / N) * A[N];
	ans += A[K % N];
	
	cout << ans << "\n";
	
	return 0;
}