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