import numpy as np

class Solver(object):
    def __init__(self):
        self.max_depth = 0

    def puts(self, ind, muki, box, n, depth=0):
        i = ind // n
        j = ind % n
        if box[i, j] != 0:
            if not ind == n**2-1:
                self.puts(ind+1, 0, box, n, depth)
                self.puts(ind+1, 1, box, n, depth)
        else:
            new_box = box.copy()
            new_depth = depth
            if muki == 0:
                room = new_box[i:i+n-1, j]
            else:
                room = new_box[i, j:j+n-1]
            if room.sum() >= 1 or room.size != n-1:
                pass
            else:
                room += 1
                new_depth = depth + 1
                for k in range(ind+1, n**2):
                    self.puts(k, 0, new_box, n, new_depth)
                    self.puts(k, 1, new_box, n, new_depth)
        if self.max_depth < depth:
            self.max_depth = depth

    def solve(self, box, n):
        self.puts(0, 0, box, n)
        self.puts(0, 1, box, n)
        return self.max_depth
    
n = int(input())
box = []
for i in range(n):
    row = list(input().strip())
    row = (np.array(row)=='#').astype('i')
    box.append(row)
box = np.array(box)

solver = Solver()
ans = solver.solve(box, n)

print(str(ans)+'\n')