#include<iostream>
#include<string>
using namespace std;
int main(){
	int n, k; string s;
	cin >> n >> k >> s;
	int cnt = 0, stk = 0, p = 0;
	while (k--){
		if (p == n) p = 0;
		(stk > 0) ? stk-- : cnt++;
		stk += (int)(s[p++] - '0');
	}
	cout << cnt << endl;
}