import heapq
_ = input()
ps = list(map(int, input().split()))
qs = list(map(int, input().split()))
pqs = [(-p*q*10**-5, p/1000.0, 1-q/100.0) for p, q in zip(ps, qs) if p]
pqs.sort()
c = f = s = 1
while f > 10**-5:
  pq, p, q = pqs[0]
  f *= 1 + pq/s
  c += f
  s += pq
  heapq.heapreplace(pqs, (pq*q, p*q, q))
print(c)