import java.util.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	}

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

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	}

} Main public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	} main {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	} Scanner sc = new Scanner(System.in); sc new Scanner(System.in) double N = Double.parseDouble(sc.next()); N Double.parseDouble(sc.next()) Double.parseDouble Double sc.next() sc.next sc ArrayList<Double> list = new ArrayList<>(); list new ArrayList<>() for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		} int i = 0; int i = 0; i 0 i< N i N i++ i++ i {
			list.add(Double.parseDouble(sc.next()));
		} {
			list.add(Double.parseDouble(sc.next()));
		} list.add(Double.parseDouble(sc.next())) list.add list Double.parseDouble(sc.next()) Double.parseDouble Double sc.next() sc.next sc sc.close() sc.close sc double sum = 0; sum 0 for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		} int i = 0; int i = 0; i 0 i< N i N i++ i++ i {
			sum += 1 / list.get(i);
		} {
			sum += 1 / list.get(i);
		} sum += 1 / list.get(i) sum 1 / list.get(i) 1 list.get(i) list.get list i double ans = 1 / sum; ans 1 / sum 1 sum 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 sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	}

} public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	}

} Main
import java.util.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		double N = Double.parseDouble(sc.next());
		ArrayList<Double> list = new ArrayList<>();
		for(int i = 0; i< N; i++) {
			list.add(Double.parseDouble(sc.next()));
		}
		sc.close();

		double sum = 0;
		for(int i = 0; i< N; i++) {
			sum += 1 / list.get(i);
		}
		double ans = 1 / sum;
		System.out.println(ans);
	}

}
