import heapq
n = int(raw_input())
p = map(int, raw_input().split())
q = map(int, raw_input().split())

que = [[-p[i] * q[i] * 1.0 / 100000.0, i] for i in xrange(n)]
heapq.heapify(que)
_ans, ans = -1.0, 0.0
i = 1
while ans - _ans > 1e-6:
    _ans = ans
    pq, j = heapq.heappop(que)
    ans += -i * pq
    heapq.heappush(que, [pq * (100 - q[j]) / 100, j])
    i += 1
print "%.10f" % ans