
import java.util.Scanner;

public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	}



} import java.util.Scanner; Scanner java.util public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	}



} Main public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	} main {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	} Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int n = Integer.parseInt(scanner.nextLine()); n Integer.parseInt(scanner.nextLine()) Integer.parseInt Integer scanner.nextLine() scanner.nextLine scanner String[] temp = scanner.nextLine().split(" "); temp scanner.nextLine().split(" ") scanner.nextLine().split scanner.nextLine() scanner.nextLine scanner " " int[] list = new int[n]; list new int[n] n double ans = 0; ans 0 for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		} {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		} list[i] = Integer.parseInt(temp[i]) list[i] list i Integer.parseInt(temp[i]) Integer.parseInt Integer temp[i] temp i ans += 1.0 / list[i] ans 1.0 / list[i] 1.0 list[i] list i ans = 1 / ans ans 1 / ans 1 ans System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	}



} public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	}



} Main

import java.util.Scanner;

public class Main{

	public static void main(String[] args) {

		Scanner scanner = new Scanner(System.in);
		int n = Integer.parseInt(scanner.nextLine());

		String[] temp = scanner.nextLine().split(" ");
		int[] list = new int[n];
		double ans = 0;
		for(int i = 0; i < n; i++) {

			list[i] = Integer.parseInt(temp[i]);
			ans += 1.0 / list[i];
		}


		ans = 1 / ans;

		System.out.println(ans);







	}



}
