Problems
Regular graph
Regular graph
Undirected graph is called \textbf{regular}, if all its vertices have the same degree.
Graph is given by list of edges. Check, is it regular.
\InputFile
First line contains number $n~(1 \le n \le 100)$ of vertices and number $m~(m \le n \cdot (n - 1) / 2)$ of edges in a graph. Then given $m$ pairs of numbers --- the edges of graph.
\OutputFile
Print "\textbf{YES}" if graph is regular and "\textbf{NO}" otherwise.
\includegraphics{https://static.e-olymp.com/content/dc/dcd4c29100bedb8c5e5e23e4516b5f260f9aae44.gif}
Input example #1
3 3 1 2 1 3 2 3
Output example #1
YES
Input example #2
3 2 1 2 2 3
Output example #2
NO