class Calc0089
  EPS = 1e-5

  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @c = args.shift.first.to_i
    @ri, @ro = args.shift.map(&:to_i)
  end

  def run
    Math::PI ** 2 * @c * (@ro + @ri) * (@ro - @ri) ** 2 / 4
  end
end

puts Calc0089.new(STDIN.readlines).run if __FILE__ == $0