
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double sum = 0; sum 0 for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt(); int i = 0; int i = 0; i 0 i < n i n i ++ i ++ i sum += 1.0 / sc.nextInt(); sum += 1.0 / sc.nextInt() sum 1.0 / sc.nextInt() 1.0 sc.nextInt() sc.nextInt sc sc.close() sc.close sc sum = 1.0 / sum sum 1.0 / sum 1.0 sum System.out.println(String.format("%f", sum)) System.out.println System.out System System.out String.format("%f", sum) String.format String "%f" sum String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    }
} Main

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();

        double sum = 0;
        for(int i = 0; i < n; i ++) sum += 1.0 / sc.nextInt();
        sc.close();

        sum = 1.0 / sum;

        System.out.println(String.format("%f", sum));


    }
}
