import java.util.Scanner;
public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	}

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

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	}

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

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	} main {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int seisu = scan.nextInt(); seisu scan.nextInt() scan.nextInt scan double[] array = new double[seisu]; array new double[seisu] seisu double sum = 0; sum 0 double gyaku = 0; gyaku 0 for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		} int i=0; int i=0; i 0 i<seisu i seisu i++ i++ i {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		} {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		} array[i] = scan.nextInt() array[i] array i scan.nextInt() scan.nextInt scan sum += 1/array[i] sum 1/array[i] 1 array[i] array i gyaku = 1/sum gyaku 1/sum 1 sum System.out.println(gyaku) System.out.println System.out System System.out gyaku scan.close() scan.close scan String[] args args public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	}

} public class Main {

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	}

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

	public static void main(String[] args) {

		Scanner scan = new Scanner(System.in);

		int seisu = scan.nextInt();
		double[] array = new double[seisu];
		double sum = 0;
		double gyaku = 0;

		for(int i=0;i<seisu;i++) {
			array[i] = scan.nextInt();
			sum += 1/array[i];
		}
		gyaku = 1/sum;

		System.out.println(gyaku);
		scan.close();
	}

}
