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


public class Main {
    public static void main (String[]args)throws IOException {
        Scanner scanner = new Scanner(System.in);
        double l = scanner.nextInt();
        System.out.println(Math.pow(l/3,3));
    }
}


/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