鶸当然是做div2啦。
cpp的cout格式控制还不太熟悉，就先用C来写了。
vjudge支持的编译器很多，最好用G++，C和C++都行。因为devcpp默认带的也是GCC，这样结果和本地测试是一致的。
这题考了一点几何观察，连接所有园的圆心不难发现规律。
核心就是这一个公式。
解黄色的角所在的直角三角形即可
黄色的角为(2pi)/(2n)=pi/n
#include <stdio.h>
#include <math.h>
int main(int argc, char const *argv[])
{
const double PI=3.14159265358979323846;
double r,n,R;
scanf("%lf%lf",&n,&r);
R=r*((1/(1-sin(PI/n)))-1);
printf("%.7lf",R);
return 0;
}
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 nn and the radius of the inner circle rr. NN thinks that, using this information, you can exactly determine the radius of the outer circles RR 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.
Input
The first and the only line of the input file contains two numbers nn and rr (3≤n≤1003≤n≤100, 1≤r≤1001≤r≤100) — the number of the outer circles and the radius of the inner circle respectively.
Output
Output a single number RR — 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 10−610−6.
Formally, if your answer is aa and the jury’s answer is bb. Your answer is accepted if and only when |a−b|max(1,|b|)≤10−6|a−b|max(1,|b|)≤10−6.
Examples
Input
3 1
Output
6.4641016
Input
6 1
Output
1.0000000
Input
100 100
Output
3.2429391