import java.text.NumberFormat;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    }
} import java.text.NumberFormat; NumberFormat java.text import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    }
} Main public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    } main {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    } Scanner parameter = new Scanner(System.in); parameter new Scanner(System.in) String[] line1 = parameter.nextLine().split(" "); line1 parameter.nextLine().split(" ") parameter.nextLine().split parameter.nextLine() parameter.nextLine parameter " " String[] line2 = parameter.nextLine().split(" "); line2 parameter.nextLine().split(" ") parameter.nextLine().split parameter.nextLine() parameter.nextLine parameter " " int[] intNumber = new int[line2.length]; intNumber new int[line2.length] line2.length line2 line2.length for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        } int i = 0; int i = 0; i 0 i < line2.length i line2.length line2 line2.length i++ i++ i {

        	intNumber[i] = Integer.parseInt(line2[i]);
        } {

        	intNumber[i] = Integer.parseInt(line2[i]);
        } intNumber[i] = Integer.parseInt(line2[i]) intNumber[i] intNumber i Integer.parseInt(line2[i]) Integer.parseInt Integer line2[i] line2 i double sumNumber = 0; sumNumber 0 for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        } int nowNumber intNumber {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        } {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        } sumNumber = sumNumber + Double.valueOf(1) / nowNumber sumNumber sumNumber + Double.valueOf(1) / nowNumber sumNumber Double.valueOf(1) / nowNumber Double.valueOf(1) Double.valueOf Double 1 nowNumber double lastNumber = Double.valueOf(1) / sumNumber; lastNumber Double.valueOf(1) / sumNumber Double.valueOf(1) Double.valueOf Double 1 sumNumber System.out.println(lastNumber) System.out.println System.out System System.out lastNumber String[] args args public class Main {

	public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    }
} public class Main {

	public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    }
} Main
import java.text.NumberFormat;
import java.util.Scanner;


public class Main {

	public static void main(String[] args) {

    	Scanner parameter = new Scanner(System.in);

    	String[] line1 = parameter.nextLine().split(" ");
        String[] line2 = parameter.nextLine().split(" ");

        int[] intNumber = new int[line2.length];

        for (int i = 0; i < line2.length; i++) {

        	intNumber[i] = Integer.parseInt(line2[i]);
        }

        double sumNumber = 0;

        for (int nowNumber : intNumber) {

        	sumNumber = sumNumber + Double.valueOf(1) / nowNumber;
        }

        double lastNumber = Double.valueOf(1) / sumNumber;

        System.out.println(lastNumber);
    }
}
