import java.math.*;
import java.util.*;

	public class Main {

		public static void main(String[] args) {

			Scanner sc = new Scanner(System.in);
			int L = sc.nextInt();
			double a= L/3.0;
			double b= L/3.0;
			double v = a*b*(L-a-b);
			
			System.out.println(v);
			
		}

	}
/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