import java.util.*;

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

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    }
} import java.util.*; util.* java public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    } main {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int a = sc.nextInt(); a sc.nextInt() sc.nextInt sc float sum = 0; sum 0 int[] numarray = new int[a]; numarray new int[a] a float[] resultarray = new float[a]; resultarray new float[a] a for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        } int i = 0; int i = 0; i 0 i < a i a i++ i++ i {
            numarray[i] = sc.nextInt();
        } {
            numarray[i] = sc.nextInt();
        } numarray[i] = sc.nextInt() numarray[i] numarray i sc.nextInt() sc.nextInt sc for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        } int i = 0; int i = 0; i 0 i < numarray.length i numarray.length numarray numarray.length i++ i++ i {
            resultarray[i] = (float) 1 / numarray[i];
        } {
            resultarray[i] = (float) 1 / numarray[i];
        } resultarray[i] = (float) 1 / numarray[i] resultarray[i] resultarray i (float) 1 / numarray[i] (float) 1 numarray[i] numarray i for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        } int j = 0; int j = 0; j 0 j < resultarray.length j resultarray.length resultarray resultarray.length j++ j++ j {
            sum = sum + resultarray[j];
        } {
            sum = sum + resultarray[j];
        } sum = sum + resultarray[j] sum sum + resultarray[j] sum resultarray[j] resultarray j sum = 1 / sum sum 1 / sum 1 sum System.out.println(sum) System.out.println System.out System System.out sum String[] args args public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    }
} public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    }
} Main
import java.util.*;

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

        int a = sc.nextInt();
        float sum = 0;
        int[] numarray = new int[a];
        float[] resultarray = new float[a];
        for (int i = 0; i < a; i++) {
            numarray[i] = sc.nextInt();
        }
        for (int i = 0; i < numarray.length; i++) {
            resultarray[i] = (float) 1 / numarray[i];
        }
        for (int j = 0; j < resultarray.length; j++) {
            sum = sum + resultarray[j];
        }
        sum = 1 / sum;

        System.out.println(sum);
    }
}
