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