import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    }
} Main public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    } main {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    } 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 int[] a = new int[n]; a new int[n] n for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            a[i] = Integer.parseInt(sc.next());
        } {
            a[i] = Integer.parseInt(sc.next());
        } a[i] = Integer.parseInt(sc.next()) a[i] a i Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc double sum = 0; sum 0 for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        } int i = 0; int i = 0; i 0 i < a.length i a.length a a.length i++ i++ i {
            sum += 1.0 / a[i];
        } {
            sum += 1.0 / a[i];
        } sum += 1.0 / a[i] sum 1.0 / a[i] 1.0 a[i] a i double result = 1.0 / sum; result 1.0 / sum 1.0 sum System.out.println(result) System.out.println System.out System System.out result sc.close() sc.close sc String args[] args public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    }
} public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String args[]) {

        // 入力
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        int[] a = new int[n];
        for (int i = 0; i < n; i++) {
            a[i] = Integer.parseInt(sc.next());
        }

        // 主処理
        double sum = 0;
        for (int i = 0; i < a.length; i++) {
            sum += 1.0 / a[i];
        }

        double result = 1.0 / sum;

        // 出力
        System.out.println(result);
        sc.close();
    }
}