import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int num = Integer.valueOf(sc.nextLine()); num Integer.valueOf(sc.nextLine()) Integer.valueOf Integer sc.nextLine() sc.nextLine sc String[] values = sc.nextLine().split(" "); values sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine sc " " sc.close() sc.close sc double sum = 0; sum 0 for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        } int i = 0; int i = 0; i 0 i < num i num i++ i++ i {
            sum += 1.0 / Integer.parseInt(values[i]);
        } {
            sum += 1.0 / Integer.parseInt(values[i]);
        } sum += 1.0 / Integer.parseInt(values[i]) sum 1.0 / Integer.parseInt(values[i]) 1.0 Integer.parseInt(values[i]) Integer.parseInt Integer values[i] values i System.out.println(1.0 / sum) System.out.println System.out System System.out 1.0 / sum 1.0 sum String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
}