CF1100C.NN and the Optical Illusion

NN is an experienced internet user and that means he spends a lot of time on the social media. Once he found the following image on the Net, which asked him to compare the sizes of inner circles:

It turned out that the circles are equal. NN was very surprised by this fact, so he decided to create a similar picture himself.

He managed to calculate the number of outer circles $n$ and the radius of the inner circle $r$. NN thinks that, using this information, you can exactly determine the radius of the outer circles $R$ so that the inner circle touches all of the outer ones externally and each pair of neighboring outer circles also touches each other. While NN tried very hard to guess the required radius, he didn't manage to do that.

Help NN find the required radius for building the required picture.

NN 是一位经验丰富的互联网用户，这意味着他每天都会花费大量时间在社交媒体上。一次，他在网上发现了如下图片，要求比较内部圆的大小：

结果发现这些内部圆大小相等。NN 对这一事实感到非常惊讶，于是决定自己动手绘制一幅类似的图。

他成功计算出了外部圆的个数 $n$ 以及内部圆的半径 $r$。NN 认为，利用这些信息，可以精确确定外部圆的半径 $R$，使得：

• 内部圆与所有外部圆均外切；
• 每一对相邻的外部圆也彼此外切。

尽管 NN 尽了最大努力去猜测所需的半径 $R$，却始终未能成功。

请帮助 NN 找出构建该图形所需的半径 $R$。

The first and the only line of the input file contains two numbers $n$ and $r$ ($3 \leq n \leq 100$, $1 \leq r \leq 100$) — the number of the outer circles and the radius of the inner circle respectively.

输入文件的第一行且唯一一行包含两个数 $n$ 和 $r$（$3 \leq n \leq 100$，$1 \leq r \leq 100$），分别表示外圆的个数和内圆的半径。

Output a single number $R$ — the radius of the outer circle required for building the required picture.

Your answer will be accepted if its relative or absolute error does not exceed $10^{-6}$.

Formally, if your answer is $a$ and the jury's answer is $b$. Your answer is accepted if and only when $\frac{|a-b|}{max(1, |b|)} \le 10^{-6}$.

输出一个数字 $R$ —— 构建所需图形所需的外圆半径。

若你的答案的相对误差或绝对误差不超过 $10^{-6}$，则该答案将被接受。

形式化地，设你的答案为 $a$，评测机的答案为 $b$，则当且仅当 $\frac{|a-b|}{\max(1, |b|)} \le 10^{-6}$ 时，你的答案被接受。