import java.util.Scanner;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] sequence = new int[n];
    double denominator = 0;
    for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    }
    System.out.println(1/denominator);
  }
} import java.util.Scanner; Scanner java.util class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] sequence = new int[n];
    double denominator = 0;
    for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    }
    System.out.println(1/denominator);
  }
} Main public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] sequence = new int[n];
    double denominator = 0;
    for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    }
    System.out.println(1/denominator);
  } main {
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] sequence = new int[n];
    double denominator = 0;
    for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    }
    System.out.println(1/denominator);
  } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc int[] sequence = new int[n]; sequence new int[n] n double denominator = 0; denominator 0 for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    } {
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    } sequence[i] = sc.nextInt() sequence[i] sequence i sc.nextInt() sc.nextInt sc denominator += 1.0/sequence[i] denominator 1.0/sequence[i] 1.0 sequence[i] sequence i System.out.println(1/denominator) System.out.println System.out System System.out 1/denominator 1 denominator String[] args args
import java.util.Scanner;
class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    int n = sc.nextInt();
    int[] sequence = new int[n];
    double denominator = 0;
    for(int i = 0; i < n; i++){
      sequence[i] = sc.nextInt();
      denominator += 1.0/sequence[i];
    }
    System.out.println(1/denominator);
  }
}