

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


public class Main
{

	public static void main(String[] args)throws Exception
	{
		Scanner sc = new Scanner(System.in);
		
		Double a = sc.nextDouble();

		Double f= Math.pow(a/3, 3);
		System.out.printf("%.12f",f);
	}

}

/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