"""
 *
 * Author:  <NAME>(coderemite)
 * Email: <EMAIL>
 *
 """
X=[0,-1,0,1,0]
Y=[0,1,1,1,2]
n,*a=[*open(0)]
n=int(n)
a=[list(x) for x in a]
for r in range(n-2):
  for c in range(1,n-1):
    if all(a[r+y][c+x]=='.' for y,x in zip(Y,X)):
      for y,x in zip(Y,X):
        a[r+y][c+x]='#'
print('YNEOS'[any('.'in x for x in a)::2])
"""
 *
 * Author:  <NAME>(coderemite)
 * Email: <EMAIL>
 *
 """
X=[0,-1,0,1,0]
Y=[0,1,1,1,2]
n,*a=[*open(0)]
n=int(n)
a=[list(x) for x in a]
for r in range(n-2):
  for c in range(1,n-1):
    if all(a[r+y][c+x]=='.' for y,x in zip(Y,X)):
      for y,x in zip(Y,X):
        a[r+y][c+x]='#'
print('YNEOS'[any('.'in x for x in a)::2])
*  * Author:  <NAME>(coderemite)  * Email: <EMAIL>  *