import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    }
} import java.util.*; util.* java import java.math.*; math.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double ans=0; ans 0 for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        } {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        } double tmp = sc.nextDouble(); tmp sc.nextDouble() sc.nextDouble sc ans += (1 / tmp) ans (1 / tmp) 1 tmp System.out.println(1 / ans) System.out.println System.out System System.out 1 / ans 1 ans String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    }
} Main
import java.util.*;
import java.math.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double ans=0;
        for (int i = 0; i < n; i++) {
            double tmp = sc.nextDouble();
            ans += (1 / tmp);
        }
        System.out.println(1 / ans);
    }
}