import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int num = Integer.valueOf(sc.nextLine());
        String[] values = sc.nextLine().split(" ");
        sc.close();
        double sum = 0;
        for (int i = 0; i < num; i++) {
            sum += 1.0 / Integer.parseInt(values[i]);
        }
        System.out.println(1.0 / sum);
    }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz