Domino 2#1990
A rectangular board is given, with some of its cells cut out. Determine whether it is possible to cover all the remaining cells with domino tiles.
The first line contains two integers and (1 \le m, n \le 40) — the dimensions of the board. Each of the next lines contains characters. In these lines, the -th character of the -th line is X (uppercase Latin X) if the cell is cut out, and . (dot) if the cell is empty.
Print YES if it is possible to cover the board with domino tiles, and NO otherwise.
Example 1
Example 2