import java.util.Scanner;
public class Main{
  public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  }
} import java.util.Scanner; Scanner java.util public class Main{
  public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  }
} Main public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  } main {

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) double ans = 0; ans 0 int c = scan.nextInt(); c scan.nextInt() scan.nextInt scan for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    } int i=0; int i=0; i 0 i<c i c i++ i++ i {
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    } {
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    } double t = (double) scan.nextInt(); t (double) scan.nextInt() scan.nextInt scan ans += 1.0/t ans 1.0/t 1.0 t System.out.println(1.0/ans) System.out.println System.out System System.out 1.0/ans 1.0 ans String[]args args public class Main{
  public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  }
} public class Main{
  public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  }
} Main
import java.util.Scanner;
public class Main{
  public static void main(String[]args){

    Scanner scan = new Scanner(System.in);

    double ans = 0;
    int c = scan.nextInt();
    for(int i=0;i<c;i++){
      double t = (double) scan.nextInt();
      ans += 1.0/t;
    }
    
    System.out.println(1.0/ans);
  }
}