#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <sstream>
#include <cstring>
#include <string>
#include <vector>

#define rep(x,to) for(int (x)=0;(x)<(to);(x)++)

using namespace std;
typedef long long ll;



int main()
{
	int n, k; string s;  
	cin >> n >> k >>s;
	int at=0, res=0;
	
	rep(i,n) at += s[i]-'0';
	
	int wt = max(0, (k-5000)/n);
	res = max(0, wt * (n-at));
	at =0; k -= n * wt;
	while(k>0){
		rep(i,n){
			if(at>0) at--; else res++;
			k--; if(k < 1) break;
			at += s[i] -'0';
		}
	}
	cout << res << endl; 
	return 0;
}