import java.util.Scanner;

/**
 * @author nakker
 */

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

        float result = 0f;
        for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        }
        System.out.println(1 / result);
    }
} import java.util.Scanner; Scanner java.util class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();

        float result = 0f;
        for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        }
        System.out.println(1 / result);
    }
} Main public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();

        float result = 0f;
        for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        }
        System.out.println(1 / result);
    } main {
        Scanner scanner = new Scanner(System.in);
        int count = scanner.nextInt();

        float result = 0f;
        for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        }
        System.out.println(1 / result);
    } Scanner scanner = new Scanner(System.in); scanner new Scanner(System.in) int count = scanner.nextInt(); count scanner.nextInt() scanner.nextInt scanner float result = 0f; result 0f for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        } int i = 0; int i = 0; i 0 i < count i count i++ i++ i {
            result += 1 / scanner.nextFloat();
        } {
            result += 1 / scanner.nextFloat();
        } result += 1 / scanner.nextFloat() result 1 / scanner.nextFloat() 1 scanner.nextFloat() scanner.nextFloat scanner System.out.println(1 / result) System.out.println System.out System System.out 1 / result 1 result String[] args args
import java.util.Scanner;

/**
 * @author nakker
 */

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

        float result = 0f;
        for (int i = 0; i < count; i++) {
            result += 1 / scanner.nextFloat();
        }
        System.out.println(1 / result);
    }
}
