import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String l1 = scan.nextLine();
        scan.close();

        int L = Integer.valueOf(l1);
        double side = L / 3.0;
        System.out.println(String.format("%.12f", side * side * side));
	}
}
/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