import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    }
} import java.util.Scanner; Scanner java.util public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    }
} Main public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    } main {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    } try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        } {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        } Scanner in = new Scanner(System.in) Scanner in = new Scanner(System.in) new Scanner(System.in) int N = in.nextInt(); N in.nextInt() in.nextInt in int[] A = new int[N]; A new int[N] N for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
                A[i] = in.nextInt();
            } {
                A[i] = in.nextInt();
            } A[i] = in.nextInt() A[i] A i in.nextInt() in.nextInt in double sumInverse = 0; sumInverse 0 for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
                sumInverse += 1.0 / A[i];
            } {
                sumInverse += 1.0 / A[i];
            } sumInverse += 1.0 / A[i] sumInverse 1.0 / A[i] 1.0 A[i] A i System.out.println(1.0 / sumInverse) System.out.println System.out System System.out 1.0 / sumInverse 1.0 sumInverse String[] args args public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    }
} public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    }
} Main
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        try (Scanner in = new Scanner(System.in)) {
            int N = in.nextInt();
            int[] A = new int[N];
            for (int i = 0; i < N; i++) {
                A[i] = in.nextInt();
            }

            double sumInverse = 0;
            for (int i = 0; i < N; i++) {
                sumInverse += 1.0 / A[i];
            }
            System.out.println(1.0 / sumInverse);
        }
    }
}
