import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int num = Integer.parseInt(sc.next());
		
		double ans = (double)num * (double)num * (double)num / 27d;
		
		System.out.println(ans);
		
	}
} import java.util.*; util.* java class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int num = Integer.parseInt(sc.next());
		
		double ans = (double)num * (double)num * (double)num / 27d;
		
		System.out.println(ans);
		
	}
} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int num = Integer.parseInt(sc.next());
		
		double ans = (double)num * (double)num * (double)num / 27d;
		
		System.out.println(ans);
		
	} main {
		Scanner sc = new Scanner(System.in);
		
		int num = Integer.parseInt(sc.next());
		
		double ans = (double)num * (double)num * (double)num / 27d;
		
		System.out.println(ans);
		
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int num = Integer.parseInt(sc.next()); num Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc double ans = (double)num * (double)num * (double)num / 27d; ans (double)num * (double)num * (double)num / 27d (double)num * (double)num * (double)num (double)num * (double)num * (double)num (double)num (double)num (double)num 27d System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;

class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int num = Integer.parseInt(sc.next());
		
		double ans = (double)num * (double)num * (double)num / 27d;
		
		System.out.println(ans);
		
	}
}