CF290F.Greedy Petya

普及/提高-

通过率：0%

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题目描述

Petya is an unexperienced programming contestant. Recently he has come across the following problem:

You are given a non-directed graph which consists of $n$ nodes and $m$ edges. Your task is to determine whether the graph contains a Hamiltonian path.

Petya wrote a quick bug-free code which he believes solves this problem. After that Petya decided to give this problem for April Fools Day contest. Unfortunately, Petya might have made a mistake, and it's quite possible that his algorithm is wrong. But this isn't a good excuse to leave the contest without submitting this problem, is it?

输入格式

The first line contains two integers $n,m$ $(1<=n<=20; 0<=m<=400)$ . Next $m$ lines contain pairs of integers $v_{i},u_{i}$ $(1<=v_{i},u_{i}<=n)$ .

输出格式

Follow the format of Petya's code output.

输入输出样例

输入#1
```
2 3
1 2
2 1
1 1
```
输出#1
```
Yes
```
输入#2
```
3 0
```
输出#2
```
No
```

输入#3

输出#3

No

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