import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scan= new Scanner(System.in);
        int t = scan.nextInt();
        double sum = 0;
        for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        }

        System.out.println(1/sum);
    }
} import java.util.Scanner; Scanner java.util class Main {
    public static void main(String[] args) {
        Scanner scan= new Scanner(System.in);
        int t = scan.nextInt();
        double sum = 0;
        for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        }

        System.out.println(1/sum);
    }
} Main public static void main(String[] args) {
        Scanner scan= new Scanner(System.in);
        int t = scan.nextInt();
        double sum = 0;
        for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        }

        System.out.println(1/sum);
    } main {
        Scanner scan= new Scanner(System.in);
        int t = scan.nextInt();
        double sum = 0;
        for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        }

        System.out.println(1/sum);
    } Scanner scan= new Scanner(System.in); scan new Scanner(System.in) int t = scan.nextInt(); t scan.nextInt() scan.nextInt scan double sum = 0; sum 0 for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        } int i = 0; int i = 0; i 0 i < t i t i++ i++ i {
            sum += (double) 1/scan.nextDouble();
        } {
            sum += (double) 1/scan.nextDouble();
        } sum += (double) 1/scan.nextDouble() sum (double) 1/scan.nextDouble() (double) 1 scan.nextDouble() scan.nextDouble scan System.out.println(1/sum) System.out.println System.out System System.out 1/sum 1 sum String[] args args
import java.util.Scanner;

class Main {
    public static void main(String[] args) {
        Scanner scan= new Scanner(System.in);
        int t = scan.nextInt();
        double sum = 0;
        for (int i = 0; i < t; i++) {
            sum += (double) 1/scan.nextDouble();
        }

        System.out.println(1/sum);
    }
}
