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