from heapq import heappush,heappop
n=int(raw_input())
P=map(int,raw_input().split())
Q=map(int,raw_input().split())
hq=[]
for i,p in enumerate(P):
    heappush(hq,(-p*Q[i]*1.0/100000,i))
ans=0.0
time=1
while True:
   cur,i=heappop(hq)
   ans+=-time*cur
   if -time*cur < 0.000001:
       break
   time+=1
   heappush(hq,(cur*(100-Q[i])/100,i))
print "%.10f"%ans