handle = open("test.txt", "r")
n = int(handle.readline())
a = list(map(int, handle.readline().split()))
handle.close()
r = 0.0
z = 1
s = 0
for i in range(n):
    r = r + a[i]
    z = z * a[i]

for i in range(n):
    s = s + z / a[i]

r = r + s / z

f = open('text.txt', 'w')
f.write("{:.9f}".format(r))
f.close()