import java.util.Scanner;

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

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/sum);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/sum);
    }
} Main public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/sum);
    } main {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

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

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/sum);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/sum);
    }
} Main
import java.util.Scanner;

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

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

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