Problem J. Jigsaw separation

Author:A. Klenin   Time limit:1 sec
Input file:input.txt   Memory limit:256 Mb
Output file:output.txt  

Statement

Rectangular jigsaw puzzle consists of two pieces. Each piece is a 4-connected set of square cells, each cell represented by character 'X' or 'O'.

Your program must determine whether it is possible to separate puzzle pieces by moving either of them in vertical or horizontal direction.

In the first sample it is possible to separate pieces by moving 'X' piece up and/or 'O' piece down.

Input file format

First line of input contains two integers W H. Following H lines contain W characters each — puzzle representation.

Output file format

Output must contain a single string YES or NO.

Constraints

1 ≤ W, H ≤ 100. Each piece contains at least one cell.

Sample tests

No. Input file (input.txt) Output file (output.txt)
1
4 3
XXXX
XOXO
OOOO
YES
2
3 3
XXX
XOX
XXX
NO

0.031s 0.012s 9