import java.io.*;
import java.util.*;


class Main {
    public static void main(String[] args) {
        Scanner scr = new Scanner(System.in);
//        int t = scr.nextInt();
//        while (t-- > 0)
        solve(scr);
    }


//    static void solve(Scanner scr) {
//        int n = scr.nextInt();
//        int[] a = new int[n];
//        int[] b = new int[n + 1];
//
//        for (int i = 0; i < n; i++) {
//            a[i] = scr.nextInt();
//            b[a[i]]++;
//        }
//        int s = 0;
//        for (int i = 0; i < n; i++) {
//            s += b[i] * (b[i] - 1) / 2;
//        }
//
//        for (int i = 0; i < n; i++) {
//            int c = (b[a[i]] - 1) * (b[a[i]] - 2) / 2 > 0 ? (b[a[i]] - 1) * (b[a[i]] - 2) / 2 : 0;
//            int d = (b[a[i]]) * (b[a[i]] - 1) / 2;
//            System.out.println(s - d + c);
//        }
//
//
//    }


    static void solve(Scanner scr) {
        int L = scr.nextInt();
        double a = L / 3.0;
        double d = Math.pow(a, 3);
        System.out.printf("%f", d);

    }

}




/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz