import java.util.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	}

} import java.util.ArrayList; ArrayList java.util import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	}

} Main public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	} main {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	} ArrayList<Integer> inputNumList = new ArrayList<Integer>(); inputNumList new ArrayList<Integer>() Scanner scan = new Scanner(System.in); scan new Scanner(System.in) float sum = 0; sum 0 int count = scan.nextInt(); count scan.nextInt() scan.nextInt scan for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	} int i=0; int i=0; i 0 i<count i count i++ i++ i {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	} {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	} inputNumList.add(scan.nextInt()) inputNumList.add inputNumList scan.nextInt() scan.nextInt scan sum = sum + (float)(1.0/inputNumList.get(i)) sum sum + (float)(1.0/inputNumList.get(i)) sum (float)(1.0/inputNumList.get(i)) 1.0 inputNumList.get(i) inputNumList.get inputNumList i scan.close() scan.close scan System.out.println(1.0/sum) System.out.println System.out System System.out 1.0/sum 1.0 sum String[] args args public class Main {

	public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	}

} public class Main {

	public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	}

} Main
import java.util.ArrayList;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {

		ArrayList<Integer> inputNumList = new ArrayList<Integer>();
    	Scanner scan = new Scanner(System.in);

    	float sum = 0;
    	int count = scan.nextInt();

    	for(int i=0; i<count; i++) {

        	inputNumList.add(scan.nextInt());
        	sum = sum + (float)(1.0/inputNumList.get(i));

    	}

    	scan.close();
     	System.out.println(1.0/sum);

	}

}