Appleman and Easy Task
题目描述
A. Appleman and Easy Task
time limit per test
1 secondmemory limit per test
256 megabytesinput
standard inputoutput
standard outputToastman 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.
Examples
Input
3
xxo
xox
oxx
Output
YES
Input
4
xxxo
xoxo
oxox
xxxx
Output
NO
题目来源：fps-www.educg.net-codeforce-1-2833.xml.zip；FPS 共享题包，题包内第 1501 题。保留原作者与原赛事署名。