你的任务是编写一个程序，给定了一个地图上描述，计算出可在城市置于法律的配置碉堡的最大数量。

输入文件包含一个或多个图的描述，通过一个包含数字0的信号文件的端线之后。每个地图开始描述一个包含一个正整数n的是城市的大小行 n将至多4。接下来的n行每一个描述的地图行， 。 表明一个开放的空间和一个大写的 X 表示了墙上。有在输入文件中没有空格。

-Your task is to write a program that, given a descr iption of a map, calculates the maximum number of blockhouses that can be placed in the city in a legal configuration.

The input file contains one or more map descr iptions, followed by a line containing the number 0 that signals the end of the file. Each map descr iption begins with a line containing a positive integer n that is the size of the city　n will be at most 4. The next n lines each describe one row of the map, with a　.　indicating an open space and an uppercase　X　indicating a wall. There are no spaces in the input file.