import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    }
} Main public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    } main {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int a1 = scan.nextInt(); a1 scan.nextInt() scan.nextInt scan float total = 0; total 0 float f[] = new float[10000]; f new float[10000] 10000 for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        } int i = 0; int i = 0; i 0 i < a1 i a1 i++ i++ i {
            f[i] = scan.nextFloat();
            total += 1/f[i];
        } {
            f[i] = scan.nextFloat();
            total += 1/f[i];
        } f[i] = scan.nextFloat() f[i] f i scan.nextFloat() scan.nextFloat scan total += 1/f[i] total 1/f[i] 1 f[i] f i System.out.println(1/total) System.out.println System.out System System.out 1/total 1 total String[] args args public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    }
} public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    }
} Main
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        // Your code here!
        Scanner scan = new Scanner(System.in);
        int a1 = scan.nextInt();
        float total = 0;
        float f[] = new float[10000];
        for(int i = 0; i < a1; i++){
            f[i] = scan.nextFloat();
            total += 1/f[i];
        }
        System.out.println(1/total);
    }
}
