//Resisotrs in Parallel
import java.util.*;
public class Main{
  public static void main(String[] args) {
    Scanner sc=new Scanner(System.in);
    int n=sc.nextInt();
    double data[]=new double[1000];

    for (int i=0;i<n;i++) {
      data[i]=sc.nextDouble();
    }

    /*for (int i=0;i<n;i++) {
      System.out.println(data[i]);
    }*/

    double oki=0;

    for (int i=0;i<n;i++) {
      oki=oki+(1.0/data[i]);
    }

    System.out.println(1.0/oki);

  }
}

/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