import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        Integer[] ary = new Integer[n];
        for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        }

        double ans = 0d;
        double sum = 0d;
        for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        }

        ans =  (double)1 / sum;

        System.out.println(ans);
    }
} import java.util.*; util.* java class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        Integer[] ary = new Integer[n];
        for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        }

        double ans = 0d;
        double sum = 0d;
        for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        }

        ans =  (double)1 / sum;

        System.out.println(ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        Integer[] ary = new Integer[n];
        for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        }

        double ans = 0d;
        double sum = 0d;
        for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        }

        ans =  (double)1 / sum;

        System.out.println(ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        Integer[] ary = new Integer[n];
        for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        }

        double ans = 0d;
        double sum = 0d;
        for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        }

        ans =  (double)1 / sum;

        System.out.println(ans);
    } 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 Integer[] ary = new Integer[n]; ary new Integer[n] n for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        } int i = 0; int i = 0; i 0 i < n i n ++i ++i i {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        } {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        } int tmp = Integer.parseInt(sc.next()); tmp Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc ary[i] = tmp ary[i] ary i tmp double ans = 0d; ans 0d double sum = 0d; sum 0d for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        } int i = 0; int i = 0; i 0 i < n i n ++i ++i i {
            sum += (double)1 / (double)ary[i];
        } {
            sum += (double)1 / (double)ary[i];
        } sum += (double)1 / (double)ary[i] sum (double)1 / (double)ary[i] (double)1 (double)ary[i] ary i ans =  (double)1 / sum ans (double)1 / sum (double)1 sum System.out.println(ans) System.out.println System.out System System.out ans String[] args args
import java.util.*;

class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = Integer.parseInt(sc.next());
        Integer[] ary = new Integer[n];
        for(int i = 0; i < n; ++i) {
            int tmp = Integer.parseInt(sc.next());
            ary[i] = tmp;
        }

        double ans = 0d;
        double sum = 0d;
        for(int i = 0; i < n; ++i) {
            sum += (double)1 / (double)ary[i];
        }

        ans =  (double)1 / sum;

        System.out.println(ans);
    }
}
