
import java.math.BigDecimal;
import java.util.*;
class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        System.out.println(BigDecimal.valueOf(N*N*N/27));

    }
} import java.math.BigDecimal; BigDecimal java.math import java.util.*; util.* java class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        System.out.println(BigDecimal.valueOf(N*N*N/27));

    }
} Main public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        System.out.println(BigDecimal.valueOf(N*N*N/27));

    } main {
        Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        System.out.println(BigDecimal.valueOf(N*N*N/27));

    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = sc.nextInt(); N sc.nextInt() sc.nextInt sc System.out.println(BigDecimal.valueOf(N*N*N/27)) System.out.println System.out System System.out BigDecimal.valueOf(N*N*N/27) BigDecimal.valueOf BigDecimal N*N*N/27 N*N*N N*N*N N N N 27 String args[] args

import java.math.BigDecimal;
import java.util.*;
class Main{
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        double N = sc.nextInt();
        System.out.println(BigDecimal.valueOf(N*N*N/27));

    }
}