import java.math.BigDecimal;
import java.util.Scanner;

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

public class Main {
    public static void main(String[] args){
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        Float[] b = new Float[a];
        float sum = 0;
        for (int i = 0; i < a; i++){
            b[i] = sc.nextFloat();
        }
        for (int i = 0; i < a; i++){
            sum = sum + (1/b[i]);
        }
        System.out.print(1/sum);
    }
}
