e-olymp

Connectivity

Check whether the given undirected graph is connected. That its possible to go from any vertex to any other along the edges of this graph.

Input

The first line contains the numbers n and m are separated by spaces - the number of vertices in the graph, respectively (1n100, 1m10000). The following m lines contain two numbers ui and vi by a space (1ui, vin); each such line means that the graph there is an edge between vertices ui and vi.

Output

Print "YES", if the graph is connected, and "NO" otherwise.

Time limit 1 second
Memory limit 128 MiB
Input example #1
3 2
1 2
3 2
Output example #1
YES
Input example #2
3 1
1 3
Output example #2
NO