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

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    }
} import java.math.BigDecimal; BigDecimal java.math import java.math.MathContext; MathContext java.math import java.math.RoundingMode; RoundingMode java.math import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    }
} Main public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    } main {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.next()); N Integer.parseInt(sc.next()) Integer.parseInt Integer sc.next() sc.next sc BigDecimal sum = BigDecimal.ZERO; sum BigDecimal.ZERO BigDecimal BigDecimal.ZERO for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        } {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        } BigDecimal n = new BigDecimal(sc.next()); n new BigDecimal(sc.next()) n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN) n BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN) BigDecimal.ONE.divide BigDecimal.ONE BigDecimal BigDecimal.ONE n 7 RoundingMode.HALF_EVEN RoundingMode RoundingMode.HALF_EVEN sum = sum.add(n, MathContext.UNLIMITED) sum sum.add(n, MathContext.UNLIMITED) sum.add sum n MathContext.UNLIMITED MathContext MathContext.UNLIMITED System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString()) System.out.println System.out System System.out BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString() BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN) BigDecimal.ONE.divide BigDecimal.ONE BigDecimal BigDecimal.ONE sum 6 RoundingMode.HALF_EVEN RoundingMode RoundingMode.HALF_EVEN sc.close() sc.close sc String[] args args public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    }
} public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    }
} Main
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int N = Integer.parseInt(sc.next());
        BigDecimal sum = BigDecimal.ZERO;
        for (int i = 0; i < N; i++) {
            BigDecimal n = new BigDecimal(sc.next());
            n = BigDecimal.ONE.divide(n, 7, RoundingMode.HALF_EVEN);
            sum = sum.add(n, MathContext.UNLIMITED);
        }

        System.out.println(BigDecimal.ONE.divide(sum, 6, RoundingMode.HALF_EVEN).toPlainString());
        sc.close();
    }
}