import java.util.*;
import java.io.*;
public class Main{
  public static void main(String[] args) throws Exception{
Scanner sc = new Scanner(System.in);
    int s = sc.nextInt();
    float l = s/3f;
    
    System.out.println(l*l*l);
    
    
  }
}

/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