Problem

Find the area of ​​a regular N / K polygon inscribed in a circle with a radius of 1.

However, a regular N / K polygon is defined as "the outermost figure that takes N points on the circumference at equal intervals and connects each point every K-1".

For example, a 5/2 polygon can be drawn as follows. First, take five points at equal intervals on the circumference of radius 1.

Sample Input 2 diagram


Next, connect each point every other 2-1 = 1.

Sample Input 2 diagram


The outermost figure is a regular 5/2 square.

Sample Input 2 diagram

Constraints

The input satisfies the following constraints.

* 5 ≤ N ≤ 106
* 1 <K <N / 2
* N and K are integers that are relatively prime

Input

The input is given in the following format.


N K


Two integers N and K are given on one line.

Output

Output the area of ​​a regular N / K polygon inscribed in a circle with a radius of 1 on one line. An error of 10-5 or less is acceptable.

Examples

Input

5 2


Output

1.12256994


Input

20 3


Output

2.93114293


Input

7 3


Output

1.08395920


Input

100000 3


Output

3.14159265
#include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=a;i<b;i++)
#define REP(i,b) FOR(i,0,b)
#define MP make_pair
#define PB push_back

using ll=long long;
using pii=pair<int,int>;
using vi=vector<int>;
using ld=long double;

int read(){
	int i;
	scanf("%d",&i);
	return i;
}

int main(){
	ld n=read(),k=read();
	ld ans=sin(M_PI*2.0/n)/2;
	ld a=sin(M_PI/n);
	ld b=a/tan(M_PI*(0.5-(k-1)/n));
	ans-=a*b;
	cout<<fixed<<setprecision(10)<<ans*n<<endl;
}