def donut_taiseki(r_in, r_out)
  r_in = r_in.to_f
  r_out = r_out.to_f

  r = (r_out - r_in) / 2

  return Math::PI * r * r * (r_out + r_in) * Math::PI
end

c = gets.to_i
r_in, r_out = gets.split.map(&:to_i)
cal = donut_taiseki(r_in, r_out) * c
puts cal