
import java.util.Scanner;

public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    }
    
} import java.util.Scanner; Scanner java.util public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    }
    
} Main /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    } main {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    } Scanner s = new Scanner(System.in); s new Scanner(System.in) int n = s.nextInt(); n s.nextInt() s.nextInt s double pSum = 0; pSum 0 for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        } int i = 0; int i = 0; i 0 i < n i n i ++ i ++ i {
            int in = s.nextInt();
            pSum += 1.0 / in;
        } {
            int in = s.nextInt();
            pSum += 1.0 / in;
        } int in = s.nextInt(); in s.nextInt() s.nextInt s pSum += 1.0 / in pSum 1.0 / in 1.0 in System.out.println(1.0 / pSum) System.out.println System.out System System.out 1.0 / pSum 1.0 pSum String[] args args public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    }
    
} public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    }
    
} Main

import java.util.Scanner;

public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        
        Scanner s = new Scanner(System.in);
        int n = s.nextInt();
        
        double pSum = 0;
        
        for (int i = 0; i < n; i ++) {
            int in = s.nextInt();
            pSum += 1.0 / in;
        }
        
        System.out.println(1.0 / pSum);
    }
    
}
