
import java.util.*;

public class Main {
	static public void main(String args[]){
		Scanner sc=new Scanner(System.in);
		 
		 int l=sc.nextInt();
		 System.out.println((double)(l*l*l)/27);
	}
}
/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