import java.util.*

fun main(args: Array<String>) {

    val C = readLine()!!.toInt()
    val cin = Scanner(System.`in`)
    val R1 : Int = cin.nextInt()
    val R2 : Int = cin.nextInt()

    val S : Double = Math.PI * (R2 - R1) * (R2 - R1) / 4
    val V : Double = 2 * Math.PI * (R1 + R2) / 2 * S
    val Cal : Double = V * C
    println(Cal)
}