fun main(args: Array<String>) {
    solve(java.util.Scanner(System.`in`))
}

fun solve(sc: java.util.Scanner) {
    val L = sc.nextInt()

    val result = (L.toDouble() / 3) * (L.toDouble() / 3) * (L.toDouble() / 3)
    println("%f".format(result))
}
