from math import log
from scipy import optimize
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((1-q[i]) / (1-q[i]*x) for i in range(n)) - x

def f_prime(x):
	return sum((1/q[i] - 1) / ((1/q[i] - x)**2) for i in range(n)) - 1

r = optimize.newton(f, 0, fprime=f_prime)
#print(r)
ans = 0
for i in range(n):
	ans += a[i] * log((1-q[i]) / (1-q[i]*r))
print(ans)