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 Python (3.8.2) (judge verdict: Accepted)

# abc138_b.py
# https://atcoder.jp/contests/abc138/tasks/abc138_b

# B - Resistors in Parallel /
# 実行時間制限: 2 sec / メモリ制限: 1024 MB
# 配点 : 200点

# 問題文
# N個の整数の列 A1,…,ANが与えられます。
# これらの逆数の総和の逆数 1/((1/A1)+…+(1/AN))を求めてください。

# 制約
#     1≤N≤100
#     1≤Ai≤1000

# 入力
# 入力は以下の形式で標準入力から与えられる。
# N
# A1 A2 … AN

# 出力
# 11A1+…+1ANの値を表す小数 (または整数) を出力せよ。
# 出力は、ジャッジの出力との絶対誤差または相対誤差が 10−5以下のとき正解と判定される。

# 入力例 1
# 2
# 10 30

# 出力例 1
# 7.5

# 1/((1/10)+(1/30))=1/(4/30)=30/4=7.5です。
# なお、7.50001, 7.49999 などと出力しても正解と判定されます。

# 入力例 2
# 3
# 200 200 200

# 出力例 2
# 66.66666666666667

# 11200+1200+1200=13200=2003=66.6666...です。
# なお、6.66666e+1 などと出力しても正解と判定されます。

# 入力例 3
# 1
# 1000

# 出力例 3
# 1000

# 111000=1000です。
# なお、+1000.0 などと出力しても正解と判定されます。


global FLAG_LOG
FLAG_LOG = False


def log(value):
    # FLAG_LOG = True
    # FLAG_LOG = False
    if FLAG_LOG:
        print(str(value))


def calculation(lines):
    # S = lines[0]
    N = int(lines[0])
    # X, A = list(map(int, lines[0].split()))
    values = list(map(int, lines[1].split()))
    # values = list(map(int, lines[2].split()))
    # values = list()
    # for i in range(6):
    #     values.append(int(lines[i]))
    # valueses = list()
    # for i in range(M):
    #     valueses.append(list(map(int, lines[i+1].split())))

    su = 0

    for n in range(N):
        su += 1/values[n]

    return [1/su]


# 引数を取得
def get_input_lines(lines_count):
    lines = list()
    for _ in range(lines_count):
        lines.append(input())
    return lines


# テストデータ
def get_testdata(pattern):
    if pattern == 1:
        lines_input = ['2', '10 30']
        lines_export = [7.5]
    if pattern == 2:
        lines_input = ['3', '200 200 200']
        lines_export = [66.66666666666667]
    if pattern == 3:
        lines_input = ['1', '1000']
        lines_export = [1000]
    return lines_input, lines_export


# 動作モード判別
def get_mode():
    import sys
    args = sys.argv
    global FLAG_LOG
    if len(args) == 1:
        mode = 0
        FLAG_LOG = False
    else:
        mode = int(args[1])
        FLAG_LOG = True
    return mode


# 主処理
def main():
    import time
    started = time.time()
    mode = get_mode()
    if mode == 0:
        lines_input = get_input_lines(2)
    else:
        lines_input, lines_export = get_testdata(mode)

    lines_result = calculation(lines_input)

    for line_result in lines_result:
        print(line_result)

    # if mode > 0:
    #     print(f'lines_input=[{lines_input}]')
    #     print(f'lines_export=[{lines_export}]')
    #     print(f'lines_result=[{lines_result}]')
    #     if lines_result == lines_export:
    #         print('OK')
    #     else:
    #         print('NG')
    # finished = time.time()
    # duration = finished - started
    # print(f'duration=[{duration}]')


# 起動処理
if __name__ == '__main__':
    main()