import java.util.*;
import java.io.*; 

public class Main {
	
	public static void main(String... string) {
		Scanner sc = new Scanner(System.in);
		float d = sc.nextFloat();
		d = d/3; 
		System.out.println(d*d*d); 
	}
}
/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