Competitions

# Maximum flow and matchings

# Domino 2

The rectangular board is given. Some of its cells are cut. Determine is it possible to cover the remaining cells with domino tiles.

#### Input

The first line contains two integers **m** and **n** (**1** ≤ **m**, **n** ≤ **40**) - the dimensions of the board. Each of the next **m** lines contains **n** symbols. The **i**-th character of **j**-th line equals to "**X**" (Latin big **X**), if the cell is cut, and "**.**" (point) if the cell is empty.

#### Output

Print "**YES**" if its possible to cover the board with domino tiles, and "**NO**" otherwise.

Input example #1

2 3 ... XXX

Output example #1

NO

Input example #2

3 2 .X .. X.

Output example #2

YES