import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	}

	private static double solve(double l) {
		l /= 3;
		return l * l * l;
	}
} import java.io.BufferedReader; BufferedReader java.io import java.io.InputStreamReader; InputStreamReader java.io import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	}

	private static double solve(double l) {
		l /= 3;
		return l * l * l;
	}
} Main public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	} main {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	} Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in))); in new Scanner(new BufferedReader(new InputStreamReader(System.in))) int l = in.nextInt(); l in.nextInt() in.nextInt in double r = solve((double) l); r solve((double) l) solve (double) l System.out.println(r) System.out.println System.out System System.out r String[] args args private static double solve(double l) {
		l /= 3;
		return l * l * l;
	} solve {
		l /= 3;
		return l * l * l;
	} l /= 3 l 3 return l * l * l; l * l * l l * l * l l l l double l l public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	}

	private static double solve(double l) {
		l /= 3;
		return l * l * l;
	}
} public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	}

	private static double solve(double l) {
		l /= 3;
		return l * l * l;
	}
} Main
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner in = new Scanner(new BufferedReader(new InputStreamReader(System.in)));
		int l = in.nextInt();
		double r = solve((double) l);
		System.out.println(r);
	}

	private static double solve(double l) {
		l /= 3;
		return l * l * l;
	}
}