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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

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