#!/usr/bin/python3

import math

def main():
	a=3
	r_in=a/2
	r_out=(a*math.sqrt(2))/2

	inn=math.pi*r_in**2
	outt=math.pi*r_out**2

	dif=outt-inn

	print(dif)

if __name__=="__main__":
	main()