CF462A.Appleman and Easy Task

普及/提高-

通过率：0%

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题目描述

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.

输入格式

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.

输出格式

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

输入输出样例

输入#1
```
3
xxo
xox
oxx
```
输出#1
```
YES
```
输入#2
```
4
xxxo
xoxo
oxox
xxxx
```
输出#2
```
NO
```

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