#!/usr/bin/ python3.8
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines
from heapq import heapify, heappushpop

N = int(readline())
P = [int(x) / 1000 for x in readline().split()]
Q = [int(x) / 100 for x in readline().split()]

hq = [(-p*q, p, q) for p, q in zip(P, Q)]
heapify(hq)

S = 1.0
n = 0
answer = 0
while S > 1e-9:
    n += 1
    x, p, q = hq[0]
    answer += n * (-x)
    S += x
    p *= (1 - q)
    heappushpop(hq, (-p * q, p, q))
    
print(answer)