n = int(input())
*p, = map(int,input().split())
*q, = map(int,input().split())

s = 0.0
for i in range(n):
    p[i] /= 1000
    q[i] /= 100
    s += p[i]*q[i]    

from heapq import *
hq = [(-pi*qi,i) for i,(pi,qi) in enumerate(zip(p,q))]
heapify(hq)
ans = 0.0
for i in range(1,1000000):
    prob,idx = heappop(hq)        
    heappush(hq,(prob*(1.0-q[idx]),idx))
    ans -= i*prob
print(ans)