D. Almost Acyclic Graphtime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard outputYou are given a directed graph consisting of n vertices and m edges (each edge is directed, so it can be traversed in only one direction). You are allowed to remove at most one edge from it.Can you make this graph acyclic by removing at most one edge from it? A directed graph is called acyclic iff it doesn't contain any cycle (a non-empty path that starts and ends in the same vertex).InputThe first line contains two integers n and m (2 ≤ n ≤ 500, 1 ≤ m ≤ min(n(n - 1), 100000)) — the number of vertices and the number of edges, respectively.Then m lines follow. Each line contains two integers u and v denoting a directed edge going from vertex u to vertex v (1 ≤ u, v ≤ n, u ≠ v). Each ordered pair (u, v) is listed at most once (there is at most one directed edge from u to v).OutputIf it is possible to make this graph acyclic by removing at most one edge, print YES. Otherwise, print NO.ExamplesInput3 41 22 33 23 1OutputYESInput5 61 22 33 23 12 14 5OutputNONoteIn the first example you can remove edge , and the graph becomes acyclic.In the second example you have to remove at least two edges (for example,  and ) in order to make the graph acyclic.
Input3 41 22 33 23 1
OutputYES
['dfs and similar', 'graphs', '*2200']