#include "bits/stdc++.h"
using namespace std;
#define int long long
#define endl '\n'
int mod=1e9+7;
int mod2=998244353;
const int INF=1e9;

signed main(){
	int n,k;
	string s;
	cin>>n>>k>>s;
	int ans=0;
	vector<int> x;
	bool f=true;
	if(s[0]=='0'){
		f=false;
		x.push_back(0);
	}
	int tmp=1;
	for(int i=1;i<n;i++){
		if((f&&s[i]=='1')||(!f&&s[i]=='0'))tmp++;
		else{
			x.push_back(tmp);
			tmp=1;
			f=!f;
		}
	}
	x.push_back(tmp);
	tmp=0;
	int m=x.size();
	for(int i=0;i<min(k*2+1,m);i++)tmp+=x[i];
	ans=tmp;
	for(int i=min(k*2+1,m);i<m;i+=2){
		tmp+=x[i];
		tmp+=x[i+1];
		tmp-=x[i-(k*2+1)];
		tmp-=x[i+1-(k*2+1)];
		ans=max(ans,tmp);
	}
	cout<<ans<<endl;
}

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