from math import log
N = int(input())
P = [float(a) for a in input().split()]
Q = [float(a) for a in input().split()]

def f(a):
    s = a
    for p, q in zip(P, Q):
        s -= p * (1 - q) / (1 - q * a)
    return s
def calc(i):
    return log((1 - Q[i]) / (1 - Q[i] * m))

l = 0
r = 1
for _ in range(100):
    m = (l + r) / 2
    if f(m) < 0:
        l = m
    else:
        r = m

print(sum([int(a) * calc(i) for i, a in enumerate(input().split())]))