import java.util.*;
class Main
{
  public static void main(String args[])
  {
    Scanner in=new Scanner(System.in);
    double L=in.nextDouble();
    double p=(double)(L/3);
    double k=p*p*p;
    System.out.println(k);
  }
}
/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