import java.util.*;
import java.io.*;
public class Main
{
    public static void main(String args[])throws Exception
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in)); 
        PrintWriter pw=new PrintWriter(System.out);
        double max=-1;
        int dim=Integer.parseInt(br.readLine());
        //if(dim==1)
        //pw.println("0.037026");
        //else if(dim==2)
    //    pw.println("0.296274");
     //   else
      //  {
            /*for(int i=1;i<=1000;i++)
            {
                for(int j=1;j<=1000;j++)
                {
                    for(int k=1;k<=1000;k++)
                    {
                        if(i+j+k==dim)
                        {
                            max=Math.max(max,(double)i*j*k);
                        }
                    }
                }
            }*/
            pw.println(Math.pow((double)dim/3,3));
        //}
        //System.out.println(max);
        pw.flush();
        pw.close();
    }
}
/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