题目描述
Seven boys and seven girls from Athens were brought before King Minos. The evil king laughed and said "I hope you enjoy your stay in Crete".
With a loud clang, the doors behind them shut, and darkness reigned. The terrified children huddled together. In the distance they heard a bellowing, unholy roar.
Bravely, they advanced forward, to their doom.
Input
$n$ ($1 \le n \le 100$) — the dimensions of the labyrinth.
Each of the next $n$ lines contains a string of lowercase English letters of length $n$.
输入格式
见题面 Input 部分
输出格式
见题面 Output 部分
样例输入
10
atzxcodera
mzhappyayc
mineodteri
trxesonaac
mtollexcxc
hjikeoutlc
eascripsni
rgvymnjcxm
onzazwswwg
geothermal
样例输出
YES