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

r = optimize.fsolve(f, 0.1)[0]
#print(r)
ans = 0
for i in range(n):
	ans += a[i] * log((1-q[i]) / (1-q[i]*r))
print(ans)