#include <bits/stdc++.h>
using namespace std;
long long power(long long x, long long y, long long m) {
  long long temp;
  if (y == 0) return 1;
  temp = power(x, y / 2, m) % m;
  if (y % 2 == 0)
    return ((temp) * (temp)) % m;
  else
    return (((x) % m) * ((temp * temp) % m)) % m;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  char mat[n][n];
  long long cnt = 0;
  for (long long i = 0; i < n; i++) {
    string s;
    cin >> s;
    for (long long j = 0; j < n; j++) {
      mat[i][j] = s[j];
      if (mat[i][j] == '.') cnt++;
    }
  }
  for (long long i = 0; i < n; i++) {
    for (long long j = 0; j < n; j++) {
      if (mat[i][j] == '.') {
        if (j == 0)
          continue;
        else {
          if (i + 2 <= n - 1 && j + 1 <= n - 1) {
            if (mat[i + 1][j] == '.' && mat[i + 1][j - 1] == '.' &&
                mat[i + 1][j + 1] == '.' && mat[i + 2][j] == '.') {
              mat[i][j] = '#';
              mat[i + 1][j] = '#';
              mat[i + 1][j - 1] = '#';
              mat[i + 1][j + 1] = '#';
              mat[i + 2][j] = '#';
              cnt -= 5;
            }
          }
        }
      }
    }
  }
  if (cnt == 0)
    cout << "YES";
  else
    cout << "NO";
  return 0;
}
