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

        double ans= (L/3)*(L/3)*(L/3);
        System.out.println(String.format("%.8f",ans));
        }
    }
/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