import java.util.Scanner;
public class Main {
 
	public static void main(String[] args) {
 
		Scanner scan = new Scanner(System.in);
 
		int L = scan.nextInt();
      
      double b = (double) L/3;
      
        double a =0;
        a = b*b*b;
        
        System.out.println(a);
    }
}
/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