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

int solve(string S) {
  int res = 0;
  int acc = 0;
  for(char c : S) {
    if(c == 'o') {
      ++acc;
      continue;
    }
    res = max(res, acc);
    acc = 0;
  }
  res = max(res, acc);
  return res;
}

int main(){
  int D;
  cin >> D;
  
  string S1, S2;
  cin >> S1 >> S2;
  
  string S = S1 + S2;
  
  int res = 0;
  for(int i=0;i<S.size();i++){
    string C = S;
    for(int j=0;j<D;j++){
      int k = i + j;
      if(k >= C.size() || C[k] == 'o')
        break;
      C[k] = 'o';
    }
    res = max(res, solve(C));
  }
  
  cout << res << endl;
  
  return 0;
}