    import java.io.*;
	import java.util.*;
    class Main
    {
      public static void main(String args[])throws IOException
      {
        double l,x,a;
        BufferedReader input=new BufferedReader(new InputStreamReader(System.in));
        Scanner sc =new Scanner(System.in);
        l=Double.parseDouble(input.readLine());
        x=l/3;
        a=x*x*x;
        System.out.println(a);
      }
    }
/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