OnlineJudge 3 现已推出。点此体验新版：A simple problem | SDUT OnlineJudge

### A simple problem

Time Limit: 1000 ms
Memory Limit: 65536 KiB

#### Problem Description

This is a very easy problem, so I do not want to write a long description for it.

Given an undirected graph with N vertexes and M edges and a vertex S of the graph, your task is to check whether all the loops of the graph contains vertex-S.

We guarantee that the given graph has at least one loop.

#### Input

There are multiple test cases.

For each test case:The fist line is three integers N 、M and S (1 <= N <= 10000 , M <= 100000 , 1<= S <= N).

Each of the following M lines contains two integers U、V (1<= U,V <= N). It shows that there is an edge between the U-th vertex and the V-th vertex.

#### Output

For each test case,output one line containing a string “YES” or “NO” (without the quotes).

#### Sample Input

5 6 3 1 2 1 5 2 3 2 4 2 5 4 5 5 6 2 1 2 1 5 2 3 2 4 2 5 4 5

#### Sample Output

NO YES

#### Hint

#### Source

qinchuan