#include <bits/stdc++.h>
using namespace std;
const int N=1e5+10;
int n,m,arr[N],brr[N],czcs,k,ans,sum,maxx;
string s;
int main(){
	cin>>n>>k;
	cin>>s;
	s=' '+s+' ';
	int op=0,cnt=1;
	char p=s[1];
	for(int i=2;i<=n+1;i++){
		if(s[i]==p){
			cnt++;
		}else{
			op++;
			arr[op]=cnt;
			brr[op]=(p-'0');
			p=s[i];
			cnt=1;
		}
	}
	int u=1;
	for(int i=1;i<=op;i++){
		if(brr[i]==0){
			sum++;
		}
		ans+=arr[i];
		while(sum>k){
			if(brr[u]==0){
				sum--;
			}
			ans-=arr[u];
			u++;
		}
		maxx=max(maxx,ans);
	}
	cout<<maxx;
}

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