
import java.math.BigDecimal;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	}
} import java.math.BigDecimal; BigDecimal java.math import java.util.Scanner; Scanner java.util public class Main {

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	}
} Main public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	} main {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	} try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		} {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		} Scanner sc = new Scanner(System.in) Scanner sc = new Scanner(System.in) new Scanner(System.in) int n = sc.nextInt(); n sc.nextInt() sc.nextInt sc BigDecimal result = BigDecimal.ZERO; result BigDecimal.ZERO BigDecimal BigDecimal.ZERO for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			} int i = 0; int i = 0; i 0 i < n i n i++ i++ i {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			} {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			} result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP)) result result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP)) result.add result BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP) BigDecimal.ONE.divide BigDecimal.ONE BigDecimal BigDecimal.ONE sc.nextBigDecimal() sc.nextBigDecimal sc 10 BigDecimal.ROUND_HALF_UP BigDecimal BigDecimal.ROUND_HALF_UP System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP)) System.out.println System.out System System.out BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP) BigDecimal.ONE.divide BigDecimal.ONE BigDecimal BigDecimal.ONE result 10 BigDecimal.ROUND_HALF_UP BigDecimal BigDecimal.ROUND_HALF_UP String[] args args public class Main {

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	}
} public class Main {

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	}
} Main

import java.math.BigDecimal;
import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		try (Scanner sc = new Scanner(System.in)) {
			int n = sc.nextInt();
			BigDecimal result = BigDecimal.ZERO;
			for (int i = 0; i < n; i++) {
				result = result.add(BigDecimal.ONE.divide(sc.nextBigDecimal(), 10, BigDecimal.ROUND_HALF_UP));
			}
			System.out.println(BigDecimal.ONE.divide(result, 10, BigDecimal.ROUND_HALF_UP));
		}
	}
}
