import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
} Main public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    } main {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    } Scanner s = new Scanner(System.in); s new Scanner(System.in) int n=s.nextInt(); n s.nextInt() s.nextInt s List<Double> l = new ArrayList<>(); l new ArrayList<>() for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        } int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
            l.add(s.nextDouble());
        } {
            l.add(s.nextDouble());
        } l.add(s.nextDouble()) l.add l s.nextDouble() s.nextDouble s double ans=0; ans 0 for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            ans+=(1/l.get(i));
        } {
            ans+=(1/l.get(i));
        } ans+=(1/l.get(i)) ans (1/l.get(i)) 1 l.get(i) l.get l i 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 s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        int n=s.nextInt();
        List<Double> l = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            l.add(s.nextDouble());
        }
        double ans=0;
        for(int i=0;i<n;i++){
            ans+=(1/l.get(i));
        }
        System.out.println(1/ans);
    }
}