import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc float sumRevertA = 0; sumRevertA 0 for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        } {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        } float a = Float.parseFloat(sc.next()); a Float.parseFloat(sc.next()) Float.parseFloat Float sc.next() sc.next sc sumRevertA += (1f / a) sumRevertA (1f / a) 1f a System.out.println(1f / sumRevertA) System.out.println System.out System System.out 1f / sumRevertA 1f sumRevertA String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        float sumRevertA = 0;
        for (int i = 0; i < N; i++) {
            float a = Float.parseFloat(sc.next());
            sumRevertA += (1f / a);
        }

        System.out.println(1f / sumRevertA);
    }
}