import java.util.*;
public class Main  
{ 
    
    public static void main(String[] args) 
    { 
        Scanner sc =new Scanner(System.in);
        double N = sc.nextDouble();
        N = N/3;
        double d = Math.pow(N,3);
      	System.out.println(d);
    }
} 
/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