#coding: utf-8
##yuki_89
import math

c=int(raw_input())
r=map(int,raw_input().split())

rin=r[0]
rout=r[1]
r1=(rout+rin)*0.5
r2=(rout-rin)*0.5

cal=c*2.0*math.pi**2*r1*r2**2
print "%.10f" % cal