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## PT07Y - Is it a tree |

You are given an unweighted, undirected graph. Write a program to check if it's a tree topology.

### Input

The first line of the input file contains two integers *N* and *M* --- number of nodes and number of edges in the graph
(0 < *N* <= 10000, 0 <= *M* <= 20000). Next *M* lines contain *M* edges of that graph --- Each line contains a pair (*u*, *v*) means
there is an edge between node *u* and node *v* (1 <= *u*,*v* <= *N*).

### Output

Print *YES* if the given graph is a tree, otherwise print *NO*.

### Example

Input:3 2 1 2 2 3Output:YES

Added by: | Thanh-Vy Hua |

Date: | 2007-03-28 |

Time limit: | 0.5s |

Source limit: | 50000B |

Memory limit: | 1536MB |

Cluster: | Cube (Intel G860) |

Languages: | C-CLANG C C++ 4.3.2 CPP CPP14 CPP14-CLANG C99 JAVA PYTHON PYTHON3 SWIFT |

Resource: | Co-author Amber |