Complete graph#3987
An undirected graph is called complete, if any pair of distinct vertices is connected by at least one edge. Given a list of graph edges, check whether the graph is complete.
The first line contains the number of vertices n~(1 \le n \le 100) and the number of edges m~(1 \le m \le 10^4) in the graph. Then pairs of numbers are given, representing the graph edges.
Print "YES" if the graph is complete and "NO" otherwise.
Example 1