P3960 [CF989E] A Trance of Nightfall
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题目描述

There is a set $S$ of $n$ points on a coordinate plane.

Kanno starts from a point $P$ that can be chosen on the plane. $P$ is not added to $S$ if it doesn't belong to $S$. Then the following sequence of operations (altogether called a move) is repeated several times, in the given order:

  1. Choose a line $l$ such that it passes through at least two elements in $S$ and passes through Kanno's current position. If there are multiple such lines, one is chosen equiprobably.
  2. Move to one of the points that belong to $S$ and lie on $l$. The destination is chosen equiprobably among all possible ones, including Kanno's current position (if it does belong to $S$).

There are $q$ queries each consisting of two integers $(t_i, m_i)$. For each query, you're to help Kanno maximize the probability of the stopping position being the $t_i$-th element in $S$ after $m_i$ moves with a proper selection of $P$, and output this maximum probability. Note that according to rule 1, $P$ should belong to at least one line that passes through at least two points from $S$.

Input

The first line contains a positive integer $n$ ($2 \leq n \leq 200$) — the number of points in $S$.

The $i$-th of the following $n$ lines contains two space-separated integers $x_i$ and $y_i$ ($-10^4 \leq x_i, y_i \leq 10^4$) — the coordinates of the $i$-th point in $S$. The input guarantees that for all $1 \leq i \lt j \leq n$, $(x_i, y_i) \neq (x_j, y_j)$ holds.

The next line contains a positive integer $q$ ($1 \leq q \leq 200$) — the number of queries.

Each of the following $q$ lines contains two space-separated integers $t$ and $m$ ($1 \leq t_i \leq n$, $1 \leq m_i \leq 10^4$) — the index of the target point and the number of moves, respectively.

Output

Output $q$ lines each containing a decimal number — the $i$-th among them denotes the maximum probability of staying on the $t_i$-th point after $m_i$ steps, with a proper choice of starting position $P$.

Your answer will be considered correct if each number in your output differs from the corresponding one in jury's answer by at most $10^{-6}$.

Formally, let your answer be $a$, and the jury's answer be $b$. Your answer is considered correct if $|a - b| \le 10^{-6}$.

输入格式

见题面 Input 部分

输出格式

见题面 Output 部分

样例输入
5 0 0 1 3 2 2 3 1 4 4 10 1 1 2 1 3 1 4 1 5 1 3 2 3 3 3 4 3 5 3 6
样例输出
0.50000000000000000000 0.50000000000000000000 0.33333333333333331483 0.50000000000000000000 0.50000000000000000000 0.18518518518518517491 0.15226337448559670862 0.14494741655235482414 0.14332164812274550414 0.14296036624949901017
提示

The points in $S$ and possible candidates for line $l$ are depicted in the following figure.

For the first query, when $P = (-1, -3)$, $l$ is uniquely determined to be $3x = y$, and thus Kanno will move to $(0, 0)$ with a probability of $\frac 1 2$.

For the third query, when $P = (2, 2)$, $l$ is chosen equiprobably between $x + y = 4$ and $x = y$. Kanno will then move to the other four points with a probability of $\frac 1 2 \cdot \frac 1 3 = \frac 1 6$ each, or stay at $(2, 2)$ with a probability of $\frac 1 3$.