import java.util.*;
import java.lang.*;

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

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