import java.util.Scanner;
public class Main {
  public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  }
} import java.util.Scanner; Scanner java.util public class Main {
  public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  }
} Main public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  } main {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int count = scan.nextInt(); count scan.nextInt() scan.nextInt scan double sum = 0; sum 0 for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    } int i=0; int i=0; i 0 i<count&&scan.hasNextInt() i<count i count scan.hasNextInt() scan.hasNextInt scan i++ i++ i {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    } {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    } int in = scan.nextInt(); in scan.nextInt() scan.nextInt scan sum += ((double)1/(double)in) sum ((double)1/(double)in) (double)1 (double)in System.out.println(1/sum) System.out.println System.out System System.out 1/sum 1 sum String... args args public class Main {
  public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  }
} public class Main {
  public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  }
} Main
import java.util.Scanner;
public class Main {
  public static void main(String... args) {
    Scanner scan = new Scanner(System.in);
    int count = scan.nextInt();
    double sum = 0;
    for (int i=0; i<count&&scan.hasNextInt(); i++) {
      int in = scan.nextInt();
      sum += ((double)1/(double)in);
    }
    System.out.println(1/sum);
  }
}