#include <iostream>
using namespace std;

int main(){
   int ans = 0,d;
   cin >> d;
   string s = "xxxxxxxxxxxxxx",tmp;
   cin >> tmp;
   s += tmp;
   cin >> tmp;
   s += tmp;
   s += "xxxxxxxxxxxxxx";
   for(int i = 0;i < s.size();i++){
      int count = 0;
      tmp = s;
      for(int j = 0;j < d && tmp[i + j] == 'x';j++) tmp[i + j] = 'o';
      for(int j = 0;j < tmp.size();j++){
         if(tmp[j] == 'o'){
            count++;
            ans = max(ans,count);
         }else count = 0;
      }
   }
   cout << ans << endl;
}