import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        for (int i = 0; i < N; i++)
            ans += 1 / A[i];

        ans = 1 / ans;

        System.out.println(ans);

    }
} import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        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 = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        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 = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        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 = sc.nextInt(); N sc.nextInt() sc.nextInt sc float[] A = new float[N]; A new float[N] N for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat(); int i = 0; int i = 0; i 0 i < N i N i++ i++ i A[i] = sc.nextFloat(); A[i] = sc.nextFloat() A[i] A i sc.nextFloat() sc.nextFloat sc float ans = 0.0f; ans 0.0f 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] 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 = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        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 = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        for (int i = 0; i < N; i++)
            ans += 1 / A[i];

        ans = 1 / ans;

        System.out.println(ans);

    }
} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int N = sc.nextInt();
        float[] A = new float[N];

        for (int i = 0; i < N; i++)
            A[i] = sc.nextFloat();

        float ans = 0.0f;

        for (int i = 0; i < N; i++)
            ans += 1 / A[i];

        ans = 1 / ans;

        System.out.println(ans);

    }
}