It was decided in IT City to distinguish successes of local IT companies by awards in the form of stars covered with gold from one side. To order the stars it is necessary to estimate order cost that depends on the area of gold-plating. Write a program that can calculate the area of a star.

A "star" figure having *n* ≥ 5 corners where *n* is a prime number is constructed the following way. On the circle of radius *r* *n* points are selected so that the distances between the adjacent ones are equal. Then every point is connected by a segment with two maximally distant points. All areas bounded by the segments parts are the figure parts.
The only line of the input contains two integers *n* (5 ≤ *n* &lt; 10<sup class="upper-index">9</sup>, *n* is prime) and *r* (1 ≤ *r* ≤ 10<sup class="upper-index">9</sup>) — the number of the star corners and the radius of the circumcircle correspondingly.
none
7 10
108.395919545675
5 1
1.122569941449
7 1000
1083959.195456745256
11 1000000000
1061689977712182980.125000000000
999999937 1
1.047197551197
999999929 2
4.188790204786
999999929 1000000000
1047197551196597556.500000000000
603530531 585244
358676198261.124618709087
7369339 31415926
1033542520749354.968872070312
2341 5001
26190419.663812126875
import sys
def input(): return sys.stdin.readline().strip()
def getints(): return map(int, sys.stdin.readline().strip().split())    

import bisect
left = lambda l,a : bisect.bisect_left(l,a)
right = lambda l,a: bisect.bisect_right(l,a)

import math

n,r = getints()
if n >= 7
    t = 2*math.pi/n
    b = 2*r/(math.tan(3*t/2)+1/math.tan(t/2))
    ans = n*r*b/2
    print(ans)
else:
    t = 2*math.pi/n
    b = 2*r/(math.tan(t)+1/math.tan(t/2))
    ans = n*r*b/2
    print(ans)