import java.util.Scanner;
import java.util.HashMap;
import java.util.Map;
import java.util.Collections;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.lang.Math;

public class Main {

    private static Scanner sc = new Scanner(System.in);
    private static int mod = (int) 10e8 + 7;

    public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    }

} import java.util.Scanner; Scanner java.util import java.util.HashMap; HashMap java.util import java.util.Map; Map java.util import java.util.Collections; Collections java.util import java.util.List; List java.util import java.util.Arrays; Arrays java.util import java.util.ArrayList; ArrayList java.util import java.lang.Math; Math java.lang public class Main {

    private static Scanner sc = new Scanner(System.in);
    private static int mod = (int) 10e8 + 7;

    public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    }

} Main private static Scanner sc = new Scanner(System.in); sc new Scanner(System.in) private static int mod = (int) 10e8 + 7; mod (int) 10e8 + 7 (int) 10e8 7 public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    } main {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    } int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double sum = 0; sum 0 for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            sum += 1 / sc.nextDouble();
        } {
            sum += 1 / sc.nextDouble();
        } sum += 1 / sc.nextDouble() sum 1 / sc.nextDouble() 1 sc.nextDouble() sc.nextDouble sc System.out.println(1 / sum) System.out.println System.out System System.out 1 / sum 1 sum String[] args args public class Main {

    private static Scanner sc = new Scanner(System.in);
    private static int mod = (int) 10e8 + 7;

    public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    }

} public class Main {

    private static Scanner sc = new Scanner(System.in);
    private static int mod = (int) 10e8 + 7;

    public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    }

} Main
import java.util.Scanner;
import java.util.HashMap;
import java.util.Map;
import java.util.Collections;
import java.util.List;
import java.util.Arrays;
import java.util.ArrayList;
import java.lang.Math;

public class Main {

    private static Scanner sc = new Scanner(System.in);
    private static int mod = (int) 10e8 + 7;

    public static void main(String[] args) {
        int n = sc.nextInt();
        // double[] a = new double[n];
        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum += 1 / sc.nextDouble();
        }
        System.out.println(1 / sum);
    }

}
