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

#define int long long
#define rep(i,l,r) for(int i=(int)(l);i<(int)(r);i++)
#define all(x) (x).begin(),(x).end()
#define sz(x) ((int)x.size())
template<class T>bool chmax(T &a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T>bool chmin(T &a,T b){if(a>b){a=b;return 1;}return 0;}

typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;

const int inf = 1LL<<60;
const int mod = 1e9 + 7;
const double eps = 1e-9;

/*{
  }*/

signed main(){
  int d;
  cin >> d;

  string s, t;
  cin >> s >> t;
  s += t;

  int ans = 0;
  rep(i, -d, 14){
    int cnt = 0;
    rep(j, -d, 14+d){
      if(i <= j and j < i+d){
        cnt++;
      }else if(j >= 0 and s[j] == 'o'){
        cnt++;
      }else{
        chmax(ans, cnt);
        cnt = 0;
      }
    }
  }

  cout << ans << endl;

  return 0;
}