Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

Undirected graph is called complete, if any pair of its different vertices is connected with at least one edge. For a given list of graph edges, check whether it is complete.

The first line contains the number of vertices $n(1≤n≤100)$ and the number of edges $m(1≤m≤10_{4})$ in the graph. Then $m$ pairs of numbers are given — the graph edges.

Print "YES" if the graph is complete and "NO" otherwise.

Input #1

Answer #1