Semi-complete graph#5077
A directed graph is called **semi-complete** if there is at least one edge between any pair of its distinct vertices.
For a graph given by a list of edges, check if it is semi-complete.
Contains the number of vertices (1 \le n \le 100) and the number of edges (1 \le m \le n \cdot (n - 1)) in the graph. Then follows pairs of numbers - the edges of the graph.
Print **YES** if the graph is semi-complete and **NO** otherwise.
Example 1