import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,queue,copy



sys.setrecursionlimit(10**7)

inf=10**20

mod=10**9+7

dd=[(-1,0),(0,1),(1,0),(0,-1)]

ddn=[(-1,0),(-1,1),(0,1),(1,1),(1,0),(1,-1),(0,-1),(-1,-1)]



def LI(): return [int(x) for x in sys.stdin.readline().split()]

def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]

def I(): return int(sys.stdin.readline())

def LS(): return sys.stdin.readline().split()

def S(): return eval(input())



def main():

  n=I()

  l=LI()



  sm=0

  for x in l:

    sm+=1/x



  return 1/sm



# main()

print((main()))

# 入力

n=int(eval(input()))

l=list(map(int,input().split()))



# 各項の逆数の和を取る

sm=0

for x in l:

  sm+=1/x

  

# 和の逆数を出力

print((1/sm))

import math, string, itertools, fractions, heapq, collections, re, array, bisect, sys, random, time, queue, copy

sys.setrecursionlimit(10**7)
inf = 10**20
mod = 10**9 + 7
dd = [(-1, 0), (0, 1), (1, 0), (0, -1)]
ddn = [(-1, 0), (-1, 1), (0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1)]


def LI():
    return [int(x) for x in sys.stdin.readline().split()]


def LI_():
    return [int(x) - 1 for x in sys.stdin.readline().split()]


def I():
    return int(sys.stdin.readline())


def LS():
    return sys.stdin.readline().split()


def S():
    return eval(input())


def main():
    n = I()
    l = LI()
    sm = 0
    for x in l:
        sm += 1 / x
    return 1 / sm


# main()
print((main()))

# 入力
n = int(eval(input()))
l = list(map(int, input().split()))
# 各項の逆数の和を取る
sm = 0
for x in l:
    sm += 1 / x
# 和の逆数を出力
print((1 / sm))

-import math, string, itertools, fractions, heapq, collections, re, array, bisect, sys, random, time, queue, copy - -sys.setrecursionlimit(10**7) -inf = 10**20 -mod = 10**9 + 7 -dd = [(-1, 0), (0, 1), (1, 0), (0, -1)] -ddn = [(-1, 0), (-1, 1), (0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-1, -1)] - - -def LI(): -    return [int(x) for x in sys.stdin.readline().split()] - - -def LI_(): -    return [int(x) - 1 for x in sys.stdin.readline().split()] - - -def I(): -    return int(sys.stdin.readline()) - - -def LS(): -    return sys.stdin.readline().split() - - -def S(): -    return eval(input()) - - -def main(): -    n = I() -    l = LI() -    sm = 0 -    for x in l: -        sm += 1 / x -    return 1 / sm - - -# main() -print((main())) +# 入力 +n = int(eval(input())) +l = list(map(int, input().split())) +# 各項の逆数の和を取る +sm = 0 +for x in l: +    sm += 1 / x +# 和の逆数を出力 +print((1 / sm))