import java.util.*;

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

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