import java.util.Scanner;

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

public class Main{
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        double sumaFraccion = 0;
        int n = in.nextInt();
        for (int i = 0; i < n; i++) {
            double Ai= in.nextDouble();
            sumaFraccion+= 1.0/Ai;
            
        }
        double resutlado = 1/sumaFraccion;
        System.out.println(resutlado);
    }
}