#include <bits/stdc++.h>
using namespace std;
int main() {
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
long long c;
cin>>c;
string s;
cin>>s;
long long counter=1;
long long sum=0;
bool f=1;
for(int i=0;i<s.size();i++)
{
if(s[i]=='0')
{
f=0;
}
}
if(f)
{
cout<<1;
}
else{
for(int i=0;i<s.size();i++)
{
if(s[i]=='0')
{
if(sum==c)
{
break;
}
counter++;
sum=max(sum,counter);
if(sum==c)
{
break;
}
}
if(s[i]=='1'&&counter>1)
{
counter--;
}
}
cout<<sum;}
return 0;
}
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