import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    }
} Main public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    } main {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    } Scanner tan = new Scanner(System.in); tan new Scanner(System.in) while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        } tan.hasNext() tan.hasNext tan {
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        } int t=tan.nextInt(); t tan.nextInt() tan.nextInt tan double sum = 0; sum 0 double[] a = new double[t]; a new double[t] t for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            } int i = 0; int i = 0; i 0 i < t i t i++ i++ i {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            } {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            } a[i]=tan.nextDouble() a[i] a i tan.nextDouble() tan.nextDouble tan sum=sum+1/a[i] sum sum+1/a[i] sum 1/a[i] 1 a[i] a i System.out.println(1/sum) System.out.println System.out System System.out 1/sum 1 sum String[] args args public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    }
} public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner tan = new Scanner(System.in);
        while(tan.hasNext()){
            int t=tan.nextInt();
            double sum = 0;
            double[] a = new double[t];
            for (int i = 0; i < t; i++) {
                a[i]=tan.nextDouble();
                sum=sum+1/a[i];
            }
            System.out.println(1/sum);
        }
    }
}
