import java.util.*;
public class Main
{
public static void main(String[] args) {
Scanner sc=new Scanner(System.in);

double l =sc.nextDouble();
double z=(double)(l/3)*(l/3)*(l/3);
System.out.format("%.12f",z);
}

}
/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