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Problems

Complete graph

Complete graph

Time limit 1 second
Memory limit 128 MiB

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.

Input data

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 m pairs of numbers are given — the graph edges.

Output data

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

Examples

Input example #1
3 3
1 2
1 3
2 3
Output example #1
YES