Maze Path Finder

You are given a maze represented as an MxN grid. Each cell in the maze is either an open space denoted by a dot ('.') or a wall denoted by a hash ('#'). Your task is to determine if there is a valid path that starts at the top-left corner (0,0) and ends at the bottom-right corner (M-1, N-1).

A path can move one cell at a time in either the up, down, left, or right direction without moving diagonally, and cannot pass through walls.

Note: The maze may contain multiple obstacles, and if the starting cell or ending cell is blocked, then there is no valid path.

The answer should be YES if a path exists and NO otherwise.

Additionally, all formulas (if any) must be in LaTeX format.

inputFormat

The first line contains two integers M and N representing the number of rows and columns respectively.

The next M lines each contain a string of length N consisting only of '.' (open space) and '#' (wall) representing the maze.

For example:

4 4
....
.#..
.#..
....

outputFormat

Output a single line containing YES if there is a path from the top-left corner to the bottom-right corner; otherwise, output NO.

## sample

4 4
....
.#..
.#..
....

YES