#include <bits/stdc++.h>
using namespace std;
int dx[] = {0, 0, 1, -1, -1, -1, 1, 1};
int dy[] = {1, -1, 0, 0, -1, 1, 1, -1};
template <class T>
inline T biton(T n, T pos) {
  return n | ((T)1 << pos);
}
template <class T>
inline T bitoff(T n, T pos) {
  return n & ~((T)1 << pos);
}
template <class T>
inline T ison(T n, T pos) {
  return (bool)(n & ((T)1 << pos));
}
template <class T>
inline T gcd(T a, T b) {
  while (b) {
    a = a % b;
    swap(a, b);
  }
  return a;
}
template <class T>
inline T bigmod(T p, T e, T m) {
  T ret = 1;
  for (; e > 0; e >>= 1) {
    if (e & 1) ret = (ret * p) % m;
    p = (p * p) % m;
  }
  return (T)ret;
}
char board[100][100];
bool solve() {
  int n;
  cin >> n;
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      cin >> board[i][j];
    }
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 1; j <= n; j++) {
      if (board[i][j] == '.') {
        board[i][j] = '#';
        if (board[i + 1][j] != '.') {
          return false;
        }
        board[i + 1][j] = '#';
        if (board[i + 2][j] != '.') {
          return false;
        }
        board[i + 2][j] = '#';
        if (board[i + 1][j - 1] != '.') {
          return false;
        }
        board[i + 1][j - 1] = '#';
        if (board[i + 1][j + 1] != '.') {
          return false;
        }
        board[i + 1][j + 1] = '#';
      }
    }
  }
  return true;
}
int main() {
  ios_base::sync_with_stdio(false);
  cout.setf(ios::fixed);
  cout.precision(10);
  cout.tie(nullptr);
  cin.tie(nullptr);
  int t = 1;
  while (t--) {
    if (solve()) {
      cout << "YES" << endl;
    } else {
      cout << "NO" << endl;
    }
  }
  int pause;
  cin >> pause;
  return 0;
}
