import java.io.*;
import java.util.*;

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];
    
    for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    }
    
    double sum = 0;
    for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    }
    
    System.out.println(1.0/sum);
  }
} import java.io.*; io.* java import java.util.*; util.* java 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];
    
    for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    }
    
    double sum = 0;
    for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    }
    
    System.out.println(1.0/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];
    
    for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    }
    
    double sum = 0;
    for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    }
    
    System.out.println(1.0/sum);
  } main {
    Scanner sc = new Scanner(System.in);
    int N = Integer.parseInt(sc.next());
    int[] A = new int[N];
    
    for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    }
    
    double sum = 0;
    for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    }
    
    System.out.println(1.0/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 for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
      A[i] = Integer.parseInt(sc.next());
    } {
      A[i] = Integer.parseInt(sc.next());
    } A[i] = Integer.parseInt(sc.next()) A[i] A i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc double sum = 0; sum 0 for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
      sum += (1.0 / A[i]);
    } {
      sum += (1.0 / A[i]);
    } sum += (1.0 / A[i]) sum (1.0 / A[i]) 1.0 A[i] A i System.out.println(1.0/sum) System.out.println System.out System System.out 1.0/sum 1.0 sum String[] args args
import java.io.*;
import java.util.*;

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];
    
    for (int i = 0; i < N; i++) {
      A[i] = Integer.parseInt(sc.next());
    }
    
    double sum = 0;
    for (int i = 0; i < N; i++) {
      sum += (1.0 / A[i]);
    }
    
    System.out.println(1.0/sum);
  }
}