# 2019-11-17 10:52:21(JST)

import sys

# import collections

# import math

# from string import ascii_lowercase, ascii_uppercase, digits

# from bisect import bisect_left as bi_l, bisect_right as bi_r

# import itertools

from functools import reduce

# import operator as op

# import re

# import heapq

# import array

# from scipy.misc import comb # (default: exact=False)

# import numpy as np



def sum_inverses(a, b):

    return a + 1 / b



def main():

    n, *a = list(map(int, sys.stdin.read().split()))



    ans = 1 / reduce(sum_inverses, a, 0)

    print(ans)



if __name__ == "__main__":

    main()

import sys



n, *A = list(map(int, sys.stdin.read().split()))



def main():

    prod = 1

    for a in A:

        prod *= a

    

    numerator = prod

    denominator = 0

    for a in A:

        denominator += prod // a

    

    return numerator / denominator



if __name__ == '__main__':

    ans = main()

    print(ans)
# 2019-11-17 10:52:21(JST)
import sys

# import collections
# import math
# from string import ascii_lowercase, ascii_uppercase, digits
# from bisect import bisect_left as bi_l, bisect_right as bi_r
# import itertools
from functools import reduce

# import operator as op
# import re
# import heapq
# import array
# from scipy.misc import comb # (default: exact=False)
# import numpy as np
def sum_inverses(a, b):
    return a + 1 / b


def main():
    n, *a = list(map(int, sys.stdin.read().split()))
    ans = 1 / reduce(sum_inverses, a, 0)
    print(ans)


if __name__ == "__main__":
    main()

import sys

n, *A = list(map(int, sys.stdin.read().split()))


def main():
    prod = 1
    for a in A:
        prod *= a
    numerator = prod
    denominator = 0
    for a in A:
        denominator += prod // a
    return numerator / denominator


if __name__ == "__main__":
    ans = main()
    print(ans)

-# 2019-11-17 10:52:21(JST) -# import collections -# import math -# from string import ascii_lowercase, ascii_uppercase, digits -# from bisect import bisect_left as bi_l, bisect_right as bi_r -# import itertools -from functools import reduce - -# import operator as op -# import re -# import heapq -# import array -# from scipy.misc import comb # (default: exact=False) -# import numpy as np -def sum_inverses(a, b): -    return a + 1 / b +n, *A = list(map(int, sys.stdin.read().split())) -    n, *a = list(map(int, sys.stdin.read().split())) -    ans = 1 / reduce(sum_inverses, a, 0) -    print(ans) +    prod = 1 +    for a in A: +        prod *= a +    numerator = prod +    denominator = 0 +    for a in A: +        denominator += prod // a +    return numerator / denominator -    main() +    ans = main() +    print(ans)