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

public class Main
{
	public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    }
} import java.util.*; util.* java import java.io.*; io.* java public class Main
{
	public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    }
} Main public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    } main {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    } BufferedReader br = new BufferedReader(new InputStreamReader(System.in)); br new BufferedReader(new InputStreamReader(System.in)) int size = Integer.parseInt(br.readLine()); size Integer.parseInt(br.readLine()) Integer.parseInt Integer br.readLine() br.readLine br int[] arr = new int[size]; arr new int[size] size double sum=0.0; sum 0.0 StringTokenizer tokenizer1 = new StringTokenizer(br.readLine()); tokenizer1 new StringTokenizer(br.readLine()) int j=0; j 0 while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      } tokenizer1.hasMoreTokens() tokenizer1.hasMoreTokens tokenizer1 {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      } arr[j] = Integer.parseInt(tokenizer1.nextToken()) arr[j] arr j Integer.parseInt(tokenizer1.nextToken()) Integer.parseInt Integer tokenizer1.nextToken() tokenizer1.nextToken tokenizer1 j++ j double num = 0.0; num 0.0 for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      } int i=0; int i=0; i 0 i<size i size i++ i++ i {
        num = (double)arr[i];
        sum += (1.0/num);
      } {
        num = (double)arr[i];
        sum += (1.0/num);
      } num = (double)arr[i] num (double)arr[i] arr i sum += (1.0/num) sum (1.0/num) 1.0 num double ans = 1/sum; ans 1/sum 1 sum System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main
{
	public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    }
} public class Main
{
	public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    }
} Main
import java.util.*;
import java.io.*;

public class Main
{
	public static void main(String[] args)throws IOException
    {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      int size = Integer.parseInt(br.readLine());
      int[] arr = new int[size];
      double sum=0.0;
      StringTokenizer tokenizer1 = new StringTokenizer(br.readLine());
      int j=0;
      while(tokenizer1.hasMoreTokens())
      {
        arr[j] = Integer.parseInt(tokenizer1.nextToken());
        j++;
      }
      double num = 0.0;
      for(int i=0;i<size;i++)
      {
        num = (double)arr[i];
        sum += (1.0/num);
      }
      double ans = 1/sum;
      System.out.println(ans);
    }
}
