26178번 - ETA 스페셜 저지다국어

문제

You want to design a level for a computer game. The level can be described as a connected undirected graph with vertices numbered from 1ドル$ to $n$. In the game, the player's character is dropped at one of the $n$ vertices uniformly at random and their goal is to reach the exit located at vertex 1ドル$ as quickly as possible. Traversing an edge takes exactly 1ドル$ second.

Figure E.1: Illustration of Sample Output 3, a level where the average optimal time to reach vertex 1ドル$ is $\frac{7}{4}$.

The difficulty of the level is determined by the average optimal time to reach the exit. Given a target value for this average optimal time, construct a level so that this target value is reached. See Figure E.1 for an example.

입력

The input consists of:

• One line with two coprime integers $a$ and $b$ (1ドル \le a,b \le 1000$) separated by a '/', giving the desired average optimal time to reach the exit as the fraction $\frac{a}{b}$.

출력

If no connected graph with the average optimal time $\frac{a}{b}$ to reach vertex 1ドル$ exists, output "impossible". Otherwise, output one such graph in the following format:

• Two integers $n$ and $m$ (1ドル \le n, m \le 10^6$), the number of vertices and the number of edges.
• $m$ pairs of integers $u$ and $v$ (1ドル \le u,v \le n$), indicating an edge between vertices $u$ and $v$.

The graph may include self loops and parallel edges. You are given that if there exists a valid graph, then there also exists one with 1ドル \le n, m \le 10^6$.

If there are multiple valid solutions, you may output any one of them.

제한

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