import java.util.Scanner;

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

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    }
} Main public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    } main {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    } Scanner in = new Scanner(System.in); in new Scanner(System.in) int N = in.nextInt(); N in.nextInt() in.nextInt in int[] nums = new int[N]; nums new int[N] N for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            nums[i] = in.nextInt();
        } {
            nums[i] = in.nextInt();
        } nums[i] = in.nextInt() nums[i] nums i in.nextInt() in.nextInt in double sum = 0; sum 0 for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            sum += Math.pow(nums[i], -1);
        } {
            sum += Math.pow(nums[i], -1);
        } sum += Math.pow(nums[i], -1) sum Math.pow(nums[i], -1) Math.pow Math nums[i] nums i -1 1 System.out.println(Math.pow(sum, -1)) System.out.println System.out System System.out Math.pow(sum, -1) Math.pow Math sum -1 1 String[] args args public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    }
} public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int N = in.nextInt();

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    }
} Main
import java.util.Scanner;

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

        int[] nums = new int[N];
        for (int i = 0; i < N; i++) {
            nums[i] = in.nextInt();
        }

        double sum = 0;
        for (int i = 0; i < N; i++) {
            sum += Math.pow(nums[i], -1);
        }

        System.out.println(Math.pow(sum, -1));
    }
}