Time limit : 1 s | Memory limit : 32 mb |
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Submitted : 281 | Accepted : 197 |

In chess, the rook is a piece that can move any number of squares
vertically or horizontally. In this problem we will consider small
chess boards (at most 4 * 4) that can also contain walls through which
rooks cannot move. The goal is to place as many rooks on a board as
possible so that no two can capture each other. A configuration of
rooks is
** legal** provided that no two rooks are on the same
horizontal row or vertical column unless there is at least one wall
separating them.

The following image shows five pictures of the same board. The
first picture is the empty board, the second and third pictures show legal
configurations, and the fourth and fifth pictures show illegal configurations.
For this board, the maximum number of rooks in a legal configuration
is 5; the second picture shows one way to do it, but there are several
other ways.

Your task is to write a program that, given a description of a board, calculates the maximum number of rooks that can be placed on the board in a legal configuration.

4 .X.. .... XX.. .... 2 XX .X 3 .X. X.X .X. 3 ... .XX .XX 4 .... .... .... .... 0

5 1 5 2 4