from decimal import Decimal as d
from math import pi

c=d(input())
rin,rout=map(d,input().split())

if c==d("0"):
  print("0.0000000000")
else:
  a=d(str(pi))*(rout-rin)**2/4
  b=d(str(pi))*(rout+rin)
  print(a*b*c)