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