from math import log
n = int(input())
p = list(map(float, input().split()))
q = list(map(float, input().split()))
a = list(map(int, input().split()))

def f(x):
	return sum(p[i] * (1-q[i]) / (1-q[i]*x) for i in range(n)) - x

l, r = 0, 1
for _ in range(50):
	x = (l+r)/2
	if f(x) < 0:
		r = x
	else:
		l = x

ans = 0
for i in range(n):
	ans += a[i] * log((1-q[i]) / (1-q[i]*r))
print(ans)