
import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    }
} import java.util.Arrays; Arrays java.util import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    }
} Main public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    } main {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    } Scanner Ent = new Scanner(System.in); Ent new Scanner(System.in) int casos = Ent.nextInt(); casos Ent.nextInt() Ent.nextInt Ent float total = 0; total 0 for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        } int i = 0; int i = 0; i 0 i < casos i casos i++ i++ i {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        } {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        } float aux = Ent.nextInt(); aux Ent.nextInt() Ent.nextInt Ent float numero = 1 / aux; numero 1 / aux 1 aux total += numero total numero System.out.println(1/total) System.out.println System.out System System.out 1/total 1 total String[] args args public class Main {

    public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    }
} public class Main {

    public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    }
} Main

import java.util.Arrays;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner Ent = new Scanner(System.in);
        int casos = Ent.nextInt();
        float total = 0;
        for (int i = 0; i < casos; i++) {
            float aux = Ent.nextInt();
            float numero = 1 / aux;
            total += numero;
        }
        System.out.println(1/total);
    }
}