import sys

from functools import reduce

def input(): return sys.stdin.readline().rstrip()



def main():

    n = int(eval(input()))

    a_tuple = tuple(map(int, input().split()))

    a_mul = reduce(lambda a, b: a*b, a_tuple)

    print((a_mul / sum([a_mul / a for a in a_tuple])))



if __name__ == '__main__':

    main()

import sys

def input(): return sys.stdin.readline().rstrip()



def main():

    n = int(eval(input()))

    a_tuple = tuple(map(int, input().split()))

    print((1 / sum([1 / a for a in a_tuple])))



if __name__ == '__main__':

    main()

import sys
from functools import reduce


def input():
    return sys.stdin.readline().rstrip()


def main():
    n = int(eval(input()))
    a_tuple = tuple(map(int, input().split()))
    a_mul = reduce(lambda a, b: a * b, a_tuple)
    print((a_mul / sum([a_mul / a for a in a_tuple])))


if __name__ == "__main__":
    main()

import sys


def input():
    return sys.stdin.readline().rstrip()


def main():
    n = int(eval(input()))
    a_tuple = tuple(map(int, input().split()))
    print((1 / sum([1 / a for a in a_tuple])))


if __name__ == "__main__":
    main()

-from functools import reduce -    a_mul = reduce(lambda a, b: a * b, a_tuple) -    print((a_mul / sum([a_mul / a for a in a_tuple]))) +    print((1 / sum([1 / a for a in a_tuple])))