import java.util.Scanner;

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

        double[] arr = new double[n];

        for(int i = 0; i < n;i++){
            arr[i] = in.nextInt();
        }

        double sum = 0;

        for(int i = 0; i < arr.length;i++){
            sum += 1/arr[i];
        }

        System.out.println(1/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