#include<iostream>
#include<string>
#include<algorithm>
#define REP(i,n) for(int i=0;i<n;++i)
using namespace std;
typedef long long LL;
int main(){
	int n, k; string s;
	cin >> n >> k >> s;

	int at = 0;
	REP(i, n) at += s[i] - '0';

	int wt = max(0, (k - 5000) / n);
	int res = max(0, wt * (n - at));
	at = 0;
	k -= n * wt;

	while (k>0){
		REP(i, n){
			(at > 0) ? at-- : res++;
			--k;
			if (k < 1) break;
			at += s[i] - '0';
		}
	}
	cout << res << endl;
	return 0;
}