import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

/**
 *
 * @author wnqmw
 */
public class Main {
    public static void main(String args[]) throws IOException {
        BufferedReader kb = new BufferedReader(new InputStreamReader(System.in));
        
        double dim = Double.parseDouble(kb.readLine());
        
        double side = dim/3;
        System.out.println(Math.pow(side, 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