#include <bits/stdc++.h>
using namespace std;
int main() {
int k;
cin>>k;
int temp=k;
int maxlength1=0;
int maxlength2=0;
string s;
cin>>s;
int start=0;
for(int i=0;i<s.length();i++)
{
if(s[i]=='b')
{
if(temp>0)
temp--;
else
{
int currlength=i-start;
maxlength1=max(currlength,maxlength1);
while(s[start]!='b')
start++;
start=start+1;
temp=temp+1;
}
}
int currlength=i-start+1;
maxlength1=max(maxlength1,currlength);
}
int start2=0;
for(int i=0;i<s.length();i++)
{
if(s[i]=='a')
{
if(k>0)
k--;
else
{
int currlength=i-start2;
maxlength2=max(currlength,maxlength2);
while(s[start2]!='a')
start2++;
start2=start2+1;
k=k+1;
}
}
int currlength=i-start2+1;
maxlength2=max(maxlength2,currlength);
}
cout<<max(maxlength1,maxlength2);
}