import java.util.Scanner;

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 sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    }
} 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();
        double[] A = new double[N];
        double sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        double[] A = new double[N];
        double sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    } main {
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        double[] A = new double[N];
        double sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    } 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 sum = 0; sum 0 for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        } int i=0; int i=0; i 0 i<N i N i++ i++ i {
            A[i] = sc.nextDouble();
        } {
            A[i] = sc.nextDouble();
        } A[i] = sc.nextDouble() A[i] A i sc.nextDouble() sc.nextDouble sc for (int j=0; j<N; j++) {
            sum += 1/A[j];
        } int j=0; int j=0; j 0 j<N j N j++ j++ j {
            sum += 1/A[j];
        } {
            sum += 1/A[j];
        } sum += 1/A[j] sum 1/A[j] 1 A[j] A j System.out.println(1/sum) System.out.println System.out System System.out 1/sum 1 sum 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 sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    }
} 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 sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    }
} Main
import java.util.Scanner;

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 sum = 0;
        
        for (int i=0; i<N; i++) {
            A[i] = sc.nextDouble();
        }
        
        for (int j=0; j<N; j++) {
            sum += 1/A[j];
        }
        
        System.out.println(1/sum);
        
    }
}