import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    }

    private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    }

}
 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.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    }

    private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    }

} Main public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    } main {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    } Scanner sc = new Scanner(System.in); sc new Scanner(System.in) int N = Integer.parseInt(sc.nextLine()); N Integer.parseInt(sc.nextLine()) Integer.parseInt Integer sc.nextLine() sc.nextLine sc String[] an = sc.nextLine().split(" "); an sc.nextLine().split(" ") sc.nextLine().split sc.nextLine() sc.nextLine sc " " long molec = 0L; molec 0L for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        } String elm an {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        } {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        } int i = Integer.parseInt(elm); i Integer.parseInt(elm) Integer.parseInt Integer elm if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            } molec == 0L molec 0L {
                molec = gcd(i, i);
            } molec = gcd(i, i) molec gcd(i, i) gcd i i {
                molec = gcd(i, molec);
            } molec = gcd(i, molec) molec gcd(i, molec) gcd i molec long denom = 0L; denom 0L for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        } String elm an {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        } {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        } int i = Integer.parseInt(elm); i Integer.parseInt(elm) Integer.parseInt Integer elm long times = molec / i; times molec / i molec i denom += times denom times System.err.println(molec + "/" + denom) System.err.println System.err System System.err molec + "/" + denom molec + "/" + denom molec "/" denom double ans = (double) molec / (double) denom; ans (double) molec / (double) denom (double) molec (double) denom System.out.println(ans) System.out.println System.out System System.out ans String[] args args private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    } gcd {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    } long tmp; tmp long c = a; c a c *= b c b while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        } (tmp = a % b) != 0 (tmp = a % b) tmp a % b a b 0 {
            a = b;
            b = tmp;
        } a = b a b b = tmp b tmp return c / b; c / b c b long a a long b b public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    }

    private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    }

} public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    }

    private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    }

} Main
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        int N = Integer.parseInt(sc.nextLine());
        String[] an = sc.nextLine().split(" ");

        // 分母の最小公倍数を求める
        long molec = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);

            if (molec == 0L) {
                molec = gcd(i, i);
            } else {
                molec = gcd(i, molec);
            }
        }

        // 分子の計算
        long denom = 0L;
        for (String elm : an) {
            int i = Integer.parseInt(elm);
            long times = molec / i;
            denom += times;
        }

        // 答え
        System.err.println(molec + "/" + denom);
        double ans = (double) molec / (double) denom;
        System.out.println(ans);
    }

    private static long gcd(long a, long b) {
        long tmp;
        long c = a;
        c *= b;
        while ((tmp = a % b) != 0) {
            a = b;
            b = tmp;
        }
        return c / b;
    }

}

