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

int main(){
  int D;
  cin >> D;
  
  string S1, S2;
  cin >> S1 >> S2;
  
  string S = S1 + S2;
  S += "x";
  
  int res = 0;
  int acc = 0;
  
  for(char c : S){
    if(c == 'o'){
      ++acc;
      continue;
    }
    res = max(res, min(D, acc));
    acc = 0;
  }
  
  cout << res << endl;
  return 0;
}