# 描述

The galaxy war between the Empire Draco and the Commonwealth of Zibu broke out 3 years ago. Draco established a line of defense called Grot. Grot is a straight line with N defense stations. Because of the cooperation of the stations, Zibu’s Marine Glory cannot march any further but stay outside the line.

A mystery Information Group X benefits form selling information to both sides of the war. Today you the administrator of Zibu’s Intelligence Department got a piece of information about Grot’s defense stations’ arrangement from Information Group X. Your task is to determine whether the information is reliable.

The information consists of M tips. Each tip is either precise or vague.

Precise tip is in the form of P A B X, means defense station A is X light-years north of defense station B.

Vague tip is in the form of V A B, means defense station A is in the north of defense station B, at least 1 light-year, but the precise distance is unknown.

## Input

There are several test cases in the input. Each test case starts with two integers $N (0 < N ≤ 1000)$ and $M (1 ≤ M ≤ 100000)$.The next $M$ line each describe a tip, either in precise form or vague form.

## Output

Output one line for each test case in the input. Output “Reliable” if It is possible to arrange $N$ defense stations satisfying all the $M$ tips, otherwise output “Unreliable”.

• intput

• output

# 思路

• $V\ A\ B$ 的情况很容易想到$Dis[A]-Dis[B]>=1 \Longrightarrow Dis[B]-Dis[A]<=-1$ 这符合了差分约束的形式，但重点是如何处理P A B X。
• $P\ A\ B\ X$的时候，将$Dis[A]-Dis[B]=x$写成
$\Longrightarrow Dis[A]-Dis[B]<=x,Dis[A]-Dis[B]>=x$
$\Longrightarrow Dis[A]-Dis[B]<=x,Dis[B]-Dis[A]<=-x$,
这样一张图就构造出来了。注意理清楚这个关系，不然太容易写错。
• 最后跑一个SPFA看看有没有负环，有就消息不可信。
• 链式向前星存图。
• 在关闭流同步的情况下，cin输入比scanf输入慢了六倍多。

# 代码

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