import java.util.*;

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

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