import random
from heapq import heappush,heappop
N=int(input())
A=[int(i) for i in input().split()]
R=[int(i) for i in input().split()]
def solve():
    ans=0
    q=[]
    for i in range(N):
        heappush(q,A[i])
        if random.randrange(2):
            ans+=heappop(q)*R[i]
    return ans

X=0
Y=0
import time
start=time.time()
while(time.time()-start<4.9):
    X+=solve()
    Y+=1
print(X/Y)