# Complete graph

Very easy

Execution time limit is 1 second

Runtime memory usage limit is 128 megabytes

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.

## Input

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, representing the graph edges.

## Output

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

## Examples

Input #1

Answer #1

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