
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    } main {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int N = scanner.nextInt(); N scanner.nextInt() scanner.nextInt scanner double answer = 0; answer 0 for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        } int i = 0 ; int i = 0 ; i 0 i < N i N i++ i++ i {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        } {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        } double A = scanner.nextDouble(); A scanner.nextDouble() scanner.nextDouble scanner answer += 1.0 / A answer 1.0 / A 1.0 A answer = 1.0 / answer answer 1.0 / answer 1.0 answer System.out.println(answer) System.out.println System.out System System.out answer String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    }
} Main

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int N = scanner.nextInt();

        double answer = 0;

        for (int i = 0 ; i < N ; i++) {
            double A = scanner.nextDouble();
            answer += 1.0 / A;
        }

        answer = 1.0 / answer;

        System.out.println(answer);
    }
}
