import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  }
} import java.util.*; util.* java public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = Integer.parseInt(sc.next()); n Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc int[] a = new int[n]; a new int[n] n double sum = 0; sum 0 for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    } int i=0; int i=0; i 0 i<n i n i++ i++ i {
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    } {
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    } a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc sum += 1.0/a[i] sum 1.0/a[i] 1.0 a[i] a i sum = 1.0 / sum sum 1.0 / sum 1.0 sum System.out.println(sum) System.out.println System.out System System.out sum String[] args args public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  }
} public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  }
} Main
import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = Integer.parseInt(sc.next());
    int[] a = new int[n];
    double sum = 0;
    for(int i=0; i<n; i++){
      a[i] = Integer.parseInt(sc.next());
      sum += 1.0/a[i];
    }

    sum = 1.0 / sum;
    System.out.println(sum);
  }
}