import java.util.Scanner

fun main(args: Array<String>){
    val scn = Scanner(System.`in`)
    val L = scn.nextLine().toInt()
    val LL = L.toFloat()
    val v = (LL/3)*(LL/3)*(LL/3)
    val result = String.format("%.12f", v)
    print("$result")
}