import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	}
} import java.util.ArrayList; ArrayList java.util import java.util.List; List java.util import java.util.Scanner; Scanner java.util public class Main {
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	}
} Main public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	} main {
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	} Scanner scan = new Scanner(System.in); scan new Scanner(System.in) int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan double temp; temp double c; c double lcm = 0; lcm 0 double top = 0; top 0 double ans = 0; ans 0 List<Integer> num = new ArrayList(); num new ArrayList() for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			int A = scan.nextInt();
			num.add(A);
		} {
			int A = scan.nextInt();
			num.add(A);
		} int A = scan.nextInt(); A scan.nextInt() scan.nextInt scan num.add(A) num.add num A for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		} int j = 0; int j = 0; j 0 j < N - 1 j N - 1 N 1 j++ j++ j {
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		} {
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		} double a = num.get(j); a num.get(j) num.get num j double b = num.get(j + 1); b num.get(j + 1) num.get num j + 1 j 1 c = a c a c *= b c b while((temp = a % b) != 0) {
				a = b;
				b = temp;
			} (temp = a % b) != 0 (temp = a % b) temp a % b a b 0 {
				a = b;
				b = temp;
			} a = b a b b = temp b temp lcm = c/b lcm c/b c b for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		} int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
			double a = num.get(i);
			top += lcm / a;
		} {
			double a = num.get(i);
			top += lcm / a;
		} double a = num.get(i); a num.get(i) num.get num i top += lcm / a top lcm / a lcm a if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		} N == 1 N 1 {
			System.out.println(num.get(0));
		} System.out.println(num.get(0)) System.out.println System.out System System.out num.get(0) num.get num 0 {
			ans = ((lcm) / (top));
			System.out.println(ans);
		} ans = ((lcm) / (top)) ans ((lcm) / (top)) (lcm) (top) System.out.println(ans) System.out.println System.out System System.out ans String[] args args public class Main {
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	}
} public class Main {
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	}
} Main
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner scan = new Scanner(System.in);
		int N = scan.nextInt();
		double temp;
		double c;
		double lcm = 0;
		double top = 0;
		double ans = 0;

		List<Integer> num = new ArrayList();

		for (int i = 0; i < N; i++){
			int A = scan.nextInt();
			num.add(A);
		}
		for (int j = 0; j < N - 1; j++){
			double a = num.get(j);
			double b = num.get(j + 1);
			c = a;
			c *= b;
			while((temp = a % b) != 0) {
				a = b;
				b = temp;
			}
			lcm = c/b;
		}

		for (int i = 0; i < N; i++){
			double a = num.get(i);
			top += lcm / a;
		}

		if (N == 1){
			System.out.println(num.get(0));
		}else {
			ans = ((lcm) / (top));
			System.out.println(ans);
		}
	}
}