import java.util.*;

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

    int n = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /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 = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /sum ;
    System.out.println(sum);
  }

} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /sum ;
    System.out.println(sum);
  } main {
    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /sum ;
    System.out.println(sum);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double[] array = new double[n]; array new double[n] n double a a sum = 0 ; sum 0 for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    } int i=0; int i=0; i 0 i<n i n i++ i++ i {
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    } {
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    } a = sc.nextInt() a sc.nextInt() sc.nextInt sc a = 1 /(double)a a 1 /(double)a 1 (double)a sum += a sum a sum = 1 /sum sum 1 /sum 1 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 = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /sum ;
    System.out.println(sum);
  }

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

    int n = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /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 = sc.nextInt();
    double[] array = new double[n];
    double a, sum = 0 ;

    for(int i=0; i<n; i++){
      a = sc.nextInt();
      a = 1 /(double)a;
      sum += a;
    }
    sum = 1 /sum ;
    System.out.println(sum);
  }

}
