Description:


liympanda, one of Ikki’s friend, likes playing games with Ikki. Today after minesweeping with Ikki and winning so many times, he is tired of such easy games and wants to play another game with Ikki.

liympanda has a magic circle and he puts it on a plane, there are n points on its boundary in circular border: 0, 1, 2, …, n − 1. Evil panda claims that he is connecting m pairs of points. To connect two points, liympanda either places the link entirely inside the circle or entirely outside the circle. Now liympanda tells Ikki no two links touch inside/outside the circle, except on the boundary. He wants Ikki to figure out whether this is possible…

Despaired at the minesweeping game just played, Ikki is totally at a loss, so he decides to write a program to help him.

Input:


The input contains exactly one test case.

In the test case there will be a line consisting of of two integers: n and m (n ≤ 1,000, m ≤ 500). The following m lines each contain two integers ai and bi, which denote the endpoints of the ith wire. Every point will have at most one link.

Output:


Output a line, either “panda is telling the truth...” or “the evil panda is lying again”.

Sample Input:


Sample Output:


题解:


题目大意:一个圆上有 \(n\) 个点(从 \(0~n-1\) 编号),给出 \(m\) 条边,你可以把一条边从圆内连过去或者从圆外连过去,求是否能够把 \(m\) 条边都连上。

可以看出这是一道2-SAT的模板题。
好久没有写过2-SAT了,发现用Tarjan比之前的方法方便很多。