## Algorithm

A. Appleman and Easy Task
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output

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.

Examples
input
Copy
`3xxoxoxoxx`
output
Copy
`YES`
input
Copy
`4xxxoxoxooxoxxxxx`
output
Copy
`NO`

## Code Examples

### #1 Code Example with C++ Programming

```Code - C++ Programming```

``````#include <bits/stdc++.h>

using namespace std;

int const N = 101;
int n;
int di[] = { 1, 0, -1, 0 };
int dj[] = { 0, 1, 0, -1 };
char g[N][N];

int main() {
scanf("%d", &n);
for(int i = 0; i < n; ++i)
scanf("%s", g[i]);

int res = 0;
for(int i = 0; i < n; ++i)
for(int j = 0, cnt = 0; j < n; ++j) {
for(int k = 0, ni, nj; k < 4; ++k) {
ni = i + di[k];
nj = j + dj[k];
if(ni >= 0 && ni < n && nj >= 0 && nj < n && g[ni][nj] == 'o')
++cnt;
}
if(cnt % 2 == 0)
++res;
}
if(res == (n * n))
puts("YES");
else
puts("NO");

return 0;
}``````
Copy The Code &

Input

cmd
3
xxo
xox
oxx

Output

cmd
YES