import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double a[] = new double[n]; a new double[n] n for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = sc.nextDouble();
        } {
            a[i] = sc.nextDouble();
        } a[i] = sc.nextDouble() a[i] a i sc.nextDouble() sc.nextDouble sc sc.close() sc.close sc double sum = 0; sum 0 for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            sum = sum + 1.0 / a[i];
        } {
            sum = sum + 1.0 / a[i];
        } sum = sum + 1.0 / a[i] sum sum + 1.0 / a[i] sum 1.0 / a[i] 1.0 a[i] a i 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) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double a[] = new double[n];
        for (int i = 0; i < n; i++) {
            a[i] = sc.nextDouble();
        }
        sc.close();

        double sum = 0;
        for (int i = 0; i < n; i++) {
            sum = sum + 1.0 / a[i];
        }

        System.out.println(1.0 / sum);
    }
}
