#include <bits/stdc++.h>
using namespace std;

template<typename T>
void chmax(T &a,T b){
  if(a<b)a=b;
}

signed main(){
  int d;cin>>d;
  string s,t;cin>>s>>t;s+=t;
  s="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"+s+"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";
  int ans=0;
  for(int i=0;i<s.size()-20;i++){
    int tmp=0;
    t=s;for(int j=i;j<i+d&&t[j]=='x';j++)t[j]='o';
    for(char p:t){
      if(p=='o')chmax(ans,++tmp);
      else tmp=0;
    }
  }
  cout<<ans<<endl;
}