
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scn  = new Scanner(System.in);
        System.out.println(maxVolume(scn.nextDouble()));
    }
    static double maxVolume(double l){
        return  l/3 * (l- l/3)/2 *(l - l/3 - (l-l/3)/2);

    }


}
// 2 4 6 8 10 12

/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