Cactus

题目描述

[problemUrl]: https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&category=17&page=show_problem&problem=1451 [PDF](https://uva.onlinejudge.org/external/105/p10510.pdf) ![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA10510/8f8ef1bc248071e829dba57f6c8e0dec8783975d.png)

输入输出格式

输入格式


![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA10510/64a7949bea41def85a0b2283b9cbcba9f8f163dc.png)

输出格式


![](https://cdn.luogu.com.cn/upload/vjudge_pic/UVA10510/979085ac359564f1fade5e9caf5c694e9cfad4e7.png)

输入输出样例

输入样例 #1

2
4
5
0 1
1 2
2 0
2 3
3 2
4
5
0 1
1 2
2 3
3 0
1 3

输出样例 #1

YES
NO