import java.util.Scanner;

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

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