Appleman and Easy Task

1000ms

262144K

Description:

Toastman came up with a very easy task. He gives it to Appleman, but Appleman doesn't know how to solve it. Can you help him?

Given a n × n checkerboard. Each cell of the board has either character 'x', or character 'o'. Is it true that each cell of the board has even number of adjacent cells with 'o'? Two cells of the board are adjacent if they share a side.

Input:

The first line contains an integer n (1 ≤ n ≤ 100). Then n lines follow containing the description of the checkerboard. Each of them contains n characters (either 'x' or 'o') without spaces.

Output:

Print "YES" or "NO" (without the quotes) depending on the answer to the problem.

Sample Input:

3
xxo
xox
oxx

Sample Output:

YES

Sample Input:

4
xxxo
xoxo
oxox
xxxx

Sample Output:

NO

Informação

Provedor Codeforces

Código CF462A