Given an m $ imes$ n matrix board where each cell is either a battleship 'X' or empty '.', return the total number of battleships on board.

Battleships can only be placed horizontally or vertically. That is, a battleship has a size of $1 imes k$ ($1$ row, $k$ columns) or $k imes 1$ ($k$ rows, $1$ column), where $k$ can be of any size. At least one horizontal or vertical empty cell separates any two battleships, meaning no two battleships are adjacent to each other.

Constraints:

• m == board.length

• n == board[i].length

• $1 \leq$ m, n $\leq 200$

• board[i][j] is either '.' or 'X'

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