import java.util.*;

public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    }
} import java.util.*; util.* java public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    } main {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc double[] a = new double[n]; a new double[n] n double bunshi = 1; bunshi 1 for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        } {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        } a[i] = sc.nextDouble() a[i] a i sc.nextDouble() sc.nextDouble sc bunshi *= a[i] bunshi a[i] a i double bunbo = 0; bunbo 0 for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        } int i=0; int i=0; i 0 i<n i n i++ i++ i {
            bunbo += bunshi / a[i];
        } {
            bunbo += bunshi / a[i];
        } bunbo += bunshi / a[i] bunbo bunshi / a[i] bunshi a[i] a i System.out.print(bunshi / bunbo) System.out.print System.out System System.out bunshi / bunbo bunshi bunbo String[] args args public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    }
} public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    }
} Main
import java.util.*;

public class Main { 
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        double[] a = new double[n];
        double bunshi = 1;
        for (int i=0; i<n; i++) {
            a[i] = sc.nextDouble();
            bunshi *= a[i];
        }
        double bunbo = 0;
        for (int i=0; i<n; i++) {
            bunbo += bunshi / a[i];
        }
        System.out.print(bunshi / bunbo);
    }
}