Undirected graph without loops and multiple edges is called transitive, if from conditions that vertices and are connected with an edge, vertices and are connected with an edge and all three vertices and are different, implies that vertices and are connected with an edge.
Verify that a given undirected graph is transitive.
The first line contains the number of vertices and edges of the graph. Then lines are given - the list of edges.
Print "YES" or "NO" — the answer to the question about transitivity of a graph.