import java.util.Scanner

import scala.io.StdIn

object Yukicoder extends App {

  val sc = new Scanner(System.in)
  val c = sc.nextDouble()
  val in = sc.nextDouble()
  val out = sc.nextDouble()

  val length = 2 * (in + out) / 2 * Math.PI
  val r = (out - in) / 2
  val S = r * r * Math.PI

  println(c * length * S)
}