import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    }
 } import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    }
 } Main public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    } main {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int first = scan.nextInt(); first scan.nextInt() scan.nextInt scan double[] inputList = new double[first]; inputList new double[first] first double[] outputList = new double[first]; outputList new double[first] first for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        } int i = 0; int i = 0; i 0 i < first i first i++ i++ i {
            inputList[i] = scan.nextInt();
        } {
            inputList[i] = scan.nextInt();
        } inputList[i] = scan.nextInt() inputList[i] inputList i scan.nextInt() scan.nextInt scan double result = 0; result 0 for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        } int j = 0; int j = 0; j 0 j < first j first j++ j++ j {
            result += 1 / inputList[j];
        } {
            result += 1 / inputList[j];
        } result += 1 / inputList[j] result 1 / inputList[j] 1 inputList[j] inputList j System.out.println(1 / result) System.out.println System.out System System.out 1 / result 1 result String[] args args public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    }
 } public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    }
 } Main
import java.util.*;
public class Main {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int first = scan.nextInt();
        double[] inputList = new double[first];
        double[] outputList = new double[first];
        
        for (int i = 0; i < first; i++) {
            inputList[i] = scan.nextInt();
        }
        
        double result = 0;
        for (int j = 0; j < first; j++) {
            result += 1 / inputList[j];
        }   
        System.out.println(1 / result);
    }
 }