import java.util.Scanner;
public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    }
  
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    }
  
} Main public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    } main {
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) final int inputNum = scan.nextInt(); inputNum scan.nextInt() scan.nextInt scan int[] values = new int[inputNum]; values new int[inputNum] inputNum float math = (float)0.0; math (float)0.0 for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        } int i = 0; int i = 0; i 0 i < inputNum i inputNum i++ i++ i {
            values[i] = scan.nextInt();
        } {
            values[i] = scan.nextInt();
        } values[i] = scan.nextInt() values[i] values i scan.nextInt() scan.nextInt scan for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        } int i = 0; int i = 0; i 0 i < inputNum i inputNum i++ i++ i {
            math += (float)1 / values[i];
        } {
            math += (float)1 / values[i];
        } math += (float)1 / values[i] math (float)1 / values[i] (float)1 values[i] values i System.out.println((float)1 / math) System.out.println System.out System System.out (float)1 / math (float)1 math scan.close() scan.close scan String[] args args public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    }
  
} public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    }
  
} Main
import java.util.Scanner;
public class Main {
    public static void main(String[] args){
        Scanner scan = new Scanner(System.in);
        final int inputNum = scan.nextInt();
        int[] values = new int[inputNum];
        float math = (float)0.0;
        for(int i = 0; i < inputNum; i++){
            values[i] = scan.nextInt();
        }
        for(int i = 0; i < inputNum; i++){
            math += (float)1 / values[i];
        }
        System.out.println((float)1 / math);
        
        scan.close();
    }
  
}