import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	}

} import java.math.BigDecimal; BigDecimal java.math import java.math.RoundingMode; RoundingMode java.math import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	}

} Main public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	} main {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) long L = sc.nextLong(); L sc.nextLong() sc.nextLong sc long bunsi = L * L * L; bunsi L * L * L L * L * L L L L double ans = bunsi / 27.0; ans bunsi / 27.0 bunsi 27.0 BigDecimal bd = new BigDecimal(ans); bd new BigDecimal(ans) System.out.println(bd.setScale(12, RoundingMode.HALF_UP)) System.out.println System.out System System.out bd.setScale(12, RoundingMode.HALF_UP) bd.setScale bd 12 RoundingMode.HALF_UP RoundingMode RoundingMode.HALF_UP String[] args args public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	}

} public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	}

} Main
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		// TODO 自動生成されたメソッド・スタブ
		Scanner sc = new Scanner(System.in);

		long L = sc.nextLong();

		long bunsi = L * L * L;
		double ans = bunsi / 27.0;

		BigDecimal bd = new BigDecimal(ans);
		System.out.println(bd.setScale(12, RoundingMode.HALF_UP));

	}

}
