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

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    }

} import java.math.BigDecimal; BigDecimal java.math import java.math.BigInteger; BigInteger java.math import java.util.Scanner; Scanner java.util public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    }

} Main public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    } main {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    } Scanner scan = new Scanner(System.in); scan new Scanner(System.in) final int N = scan.nextInt(); N scan.nextInt() scan.nextInt scan String[] array = new String[N]; array new String[N] N for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            array[i] = scan.next();
        } {
            array[i] = scan.next();
        } array[i] = scan.next() array[i] array i scan.next() scan.next scan BigInteger fraction = new BigInteger("1"); fraction new BigInteger("1") for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            fraction = fraction.multiply(new BigInteger(array[i]));
        } {
            fraction = fraction.multiply(new BigInteger(array[i]));
        } fraction = fraction.multiply(new BigInteger(array[i])) fraction fraction.multiply(new BigInteger(array[i])) fraction.multiply fraction new BigInteger(array[i]) BigInteger denominator = new BigInteger("0"); denominator new BigInteger("0") for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        } int i = 0; int i = 0; i 0 i < N i N i++ i++ i {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        } {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        } BigInteger tmp = new BigInteger("1"); tmp new BigInteger("1") for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            } int j = 0; int j = 0; j 0 j < N j N j++ j++ j {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            } {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            } if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                } j != i j i {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                } tmp = tmp.multiply(new BigInteger(array[j])) tmp tmp.multiply(new BigInteger(array[j])) tmp.multiply tmp new BigInteger(array[j]) denominator = denominator.add(tmp) denominator denominator.add(tmp) denominator.add denominator tmp BigDecimal fracDecimal = new BigDecimal(fraction); fracDecimal new BigDecimal(fraction) BigDecimal denomDecimal = new BigDecimal(denominator); denomDecimal new BigDecimal(denominator) double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue(); ans fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue() fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN) fracDecimal.divide fracDecimal denomDecimal 10 BigDecimal.ROUND_HALF_EVEN BigDecimal BigDecimal.ROUND_HALF_EVEN 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);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    }

} public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    }

} Main
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        final int N = scan.nextInt();
        String[] array = new String[N];
        for (int i = 0; i < N; i++) {
            array[i] = scan.next();
        }

        BigInteger fraction = new BigInteger("1");
        for (int i = 0; i < N; i++) {
            fraction = fraction.multiply(new BigInteger(array[i]));
        }

        BigInteger denominator = new BigInteger("0");
        for (int i = 0; i < N; i++) {
            BigInteger tmp = new BigInteger("1");
            for (int j = 0; j < N; j++) {
                if (j != i) {
                    tmp = tmp.multiply(new BigInteger(array[j]));
                }
            }
            denominator = denominator.add(tmp);
        }

        BigDecimal fracDecimal = new BigDecimal(fraction);
        BigDecimal denomDecimal = new BigDecimal(denominator);
        double ans = fracDecimal.divide(denomDecimal, 10, BigDecimal.ROUND_HALF_EVEN).doubleValue();
        System.out.println(ans);

    }

}
