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 n: usize = read();
    let mut a: Vec<f64> = read_vec();
    for i in 0..n {
        a[i] /= a[i] * a[i];
    }
    let mut ans = 0.0;
    for i in a {
        ans += i;
    }
    println!("{}", 1.0 / ans);
}





//**********************************************************************************************************************************************//

// 標準入力から一行を読み取り、指定の型に変換する関数
pub fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

// 標準入力から一行を読み取り、空白文字で分割し、各要素を指定の型に変換する関数
pub fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}

// 標準入力からn行を読み取り、各行を空白文字で分割し、各要素を指定の型に変換する関数
pub fn read_vec2<T: std::str::FromStr>(n: u64) -> Vec<Vec<T>> {
    (0..n).map(|_| read_vec()).collect()
}

// 10進数での各桁の和
pub fn sum_dights(x: isize) -> isize {
    if x % 10 == 0 {
        return 0
    }
    let m = x % 10;
    m + sum_dights((x - m) / 10)
}