import java.util.Scanner;

public class Main {
	public static void main(String args[]) {
		@SuppressWarnings("resource")
		double sum = new Scanner(System.in).nextDouble();
		
		System.out.println(Math.pow(sum / 3, 3));
		
	}
	
}
/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