import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    }
} 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();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] a = new int[n]; a new int[n] n double sum = 0; sum 0 for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        } int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        } {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        } a[i] = sc.nextInt() a[i] a i sc.nextInt() sc.nextInt sc sum += (double) 1 / a[i] sum (double) 1 / a[i] (double) 1 a[i] a i System.out.println(1.0 / sum) System.out.println System.out System System.out 1.0 / sum 1.0 sum sc.close() sc.close sc String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    }
} Main
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int[] a = new int[n];
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            a[i] = sc.nextInt();
            sum += (double) 1 / a[i];
        }
        System.out.println(1.0 / sum);
        sc.close();
    }
}