Problem:
Score : 200 points

Problem Statement

Given is a sequence of N integers A_1, \ldots, A_N.

Find the (multiplicative) inverse of the sum of the inverses of these numbers, \frac{1}{\frac{1}{A_1} + \ldots + \frac{1}{A_N}}.

Constraints

1 \leq N \leq 100

1 \leq A_i \leq 1000

Input

Input is given from Standard Input in the following format:

N
A_1 A_2 \ldots A_N

Output

Print a decimal number (or an integer) representing the value of \frac{1}{\frac{1}{A_1} + \ldots + \frac{1}{A_N}}.

Your output will be judged correct when its absolute or relative error from the judge's output is at most 10^{-5}.

Sample Input 1

2
10 30

Sample Output 1

7.5

\frac{1}{\frac{1}{10} + \frac{1}{30}} = \frac{1}{\frac{4}{30}} = \frac{30}{4} = 7.5.

Printing 7.50001, 7.49999, and so on will also be accepted.

Sample Input 2

3
200 200 200

Sample Output 2

66.66666666666667

\frac{1}{\frac{1}{200} + \frac{1}{200} + \frac{1}{200}} = \frac{1}{\frac{3}{200}} = \frac{200}{3} = 66.6666....

Printing 6.66666e+1 and so on will also be accepted.

Sample Input 3

1
1000

Sample Output 3

1000

\frac{1}{\frac{1}{1000}} = 1000.

Printing +1000.0 and so on will also be accepted.

Solution in Rust (1.15.1) (judge verdict: Accepted)

fn main() {
    let mode = "b";

    if mode == "a" {
        a::answer();
    } else if mode == "b" {
        b::answer();
    }
}
mod b {
    use std::io::*;

    pub fn answer() {
        let mut buf = String::new();

        stdin().read_to_string(&mut buf).unwrap();
        let mut ite = buf.split_whitespace();

        // 1行目読み捨て
        ite.next();

        let seq = ite.map(|x| x.parse::<i32>().unwrap()).collect::<Vec<_>>();

        let res = calc(&seq);

        println!("{}", res);
    }
    fn calc(a: &Vec<i32>) -> f64 {
        let mut bunbo_neta = 1f64;
        for i in 0..a.len() {
            bunbo_neta *= a[i] as f64;
        }
        let mut bunbo = 0f64;
        for i in 0..a.len() {
            bunbo += bunbo_neta / (a[i] as f64);
        }

        let bunshi: f64 = bunbo_neta;

        bunshi / bunbo
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        #[test]
        fn test1() {
            assert_eq!(calc(&vec![10, 30]), 7.5);
        }
        #[test]
        fn test2() {
            let res = calc(&vec![200, 200, 200]);
            assert!(res > 66.6666 && res < 66.67);
        }
        #[test]
        fn test_b_3() {
            let res = calc(&vec![1000]);
            assert!(res == 1000.0);
        }
    }
}
mod a {
    use std::io::*;

    pub fn answer() {
        let mut buf = String::new();

        stdin().read_to_string(&mut buf).unwrap();

        let mut iter = buf.split_whitespace();

        let a = iter.next().unwrap().parse::<i32>().unwrap();
        let s = iter.next().unwrap();

        let res = calc(a, s);
        println!("{}", res);
    }

    fn calc(a: i32, s: &str) -> &str {
        if a >= 3200 {
            return s;
        }
        "red"
    }

    #[cfg(test)]
    mod tests {
        use super::*;
        #[test]
        fn test1() {
            assert_eq!("pink", calc(3200, "pink"));
        }

        #[test]
        fn test2() {
            assert_eq!("red", calc(3199, "pink"));
        }

        #[test]
        fn test3() {
            assert_eq!("red", calc(4049, "red"));
        }

    }
}