Looping path

Given a directed graph with $n$ vertices and $m$ arcs, and two vertices $x$ and $y$ , is there a path that goes from $x$ to $y$ , passing through at least some other vertex at least twice? We will call this a looping path. Note that it can visit $x$ and $y$ only once (at the beginning and at the end).

Input

Input consists of several cases, each with $n$ and $m$ , followed by $m$ pairs $u$ $v$ , with $u \ne v$ , indicating an arc from $u$ to $v$ , followed by $x$ and $y$ , with $x \ne y$ . Assume $2 \le n \le 10^5$ , $0 \le m \le 5n$ , that vertices are numbered from 0 to $n-1$ , and that there are no repeated arcs.

Output

For every graph, print “YES” if there is a looping path from $x$ to $y$ , and “NO” otherwise.

Problem information

Author: Ángel García and Enrique Jiménez

Generation: 2026-01-25T10:35:39.300Z