Black and white
Description
Fernanda is playing with tiles on a board. The board is an $N\times N$ grid, with some squares painted white and others black. All squares have size 1cm $\times$ 1cm.
Fernanda will use rectangular domino tiles, of size 1cm $\times$ 2cm. She will place them in a horizontal position, occupying exactly two horizontally neighboring squares of the board.
The game imposes the rule that she can only place a domino tile on two black squares. White squares are strictly forbidden. Additionally, the same square cannot be occupied by more than one tile.
Given the colors of the $N\times N$ squares, can you help Fernanda by indicating the maximum number of tiles she can place on the board?
The first line contains an integer $N$ ($1 \leq N \leq 50$), the size of the board. $N$ lines follow describing the board. The $i$-th line contains a string of $N$ characters N or B, indicating the colors of the squares in the $i$-th row, from left to right. N for black ("Negro" in Spanish) and B for white ("Blanco" in Spanish).
A single line with an integer indicating the maximum number of tiles that can be placed on the board.
Input
The first line contains an integer $N$ ($1 \leq N \leq 50$), the size of the board. $N$ lines follow describing the board. The $i$-th line contains a string of $N$ characters N or B, indicating the colors of the squares in the $i$-th row, from left to right. N for black ("Negro" in Spanish) and B for white ("Blanco" in Spanish).
Output
A single line with an integer indicating the maximum number of tiles that can be placed on the board.
5
BNBNB
BBNNN
NNNNN
BNNNN
NNBNN
7
Note
In the example, it is possible to place $7$ tiles on the board as shown in the following figure. There is no way to place $8$ or more tiles, so the answer is $7$.
