# Rikka with Graph II

Time Limit: 2000/1000 MS (Java/Others)

Memory Limit: 65536/65536 K (Java/Others)

## Description

As we know, Rikka is poor at math. Yuta is worrying about this situation, so he gives Rikka some math tasks to practice. There is one of them:

Yuta has a non-direct graph with $n$ vertices and $n$ edges. Now he wants you to tell him if there exist a Hamiltonian path.

It is too difficult for Rikka. Can you help her?

## Input

There are no more than 100 testcases.

For each testcase, the first line contains a number $n(1 \leq n \leq 1000)$.

Then $n$ lines follow. Each line contains two numbers $u,v(1 \leq u,v \leq n)$ , which means there is an edge between $u$ and $v$.

## Output

For each testcase, if there exist a Hamiltonian path print "YES" , otherwise print "NO".

## Sample Input

4
1 1
1 2
2 3
2 4
3
1 2
2 3
3 1

## Sample Output

NO
YES

Hint
For the second testcase, One of the path is 1->2->3
If you doesn't know what is Hamiltonian path, click here (https://en.wikipedia.org/wiki/Hamiltonian_path).

hujie

## Source

BestCoder Round #53 (div.2)