from Queue import * # Queue, LifoQueue, PriorityQueue
from bisect import * #bisect, insort
from collections import * #deque, Counter,OrderedDict,defaultdict
#set([]) 
import math
import copy
import itertools
import string
import sys
myread = lambda : map(float,raw_input().split())
def solver():
    N = int(raw_input())
    P = myread()
    Q = myread()
    for i in xrange(N):
        P[i] /= 1000
        Q[i] /= 100
    
    que = PriorityQueue(N)

    for i in xrange(N):
        que.put((-P[i]*Q[i],i))
    times = 1
    ans = 0.0
    e = 0.1 ** 16
    while not(que.empty()):
        t = que.get()
        p = t[0]
        now = t[1]
        if times >= 100000:
            break
        ans += (-p) * times
        times += 1
        if (-p) * (1- Q[now]) > e:
            que.put((p*(1-Q[now]),now))

    print "%.8f" % ans
    

if __name__ == "__main__":
    solver()