import sys,random,bisect
from collections import deque,defaultdict
from heapq import heapify,heappop,heappush
from itertools import permutations
from math import gcd,log

input = lambda :sys.stdin.readline().rstrip()
mi = lambda :map(int,input().split())
li = lambda :list(mi())

N = int(input())
A = li()
R = li()

res = 0
for i in range(N):
    dp = [0 for j in range(N+1)]
    dp[0] = 1
    for j in range(i):
        ndp = [0 for k in range(N+1)]
        for k in range(N+1):
            if not dp[k]:
                continue

            if A[j] <= A[i]:
                ndp[k+1] += dp[k]/2
                ndp[k] += dp[k]/2
            else:
                if not k:
                    ndp[k] += dp[k]
                else:
                    ndp[k] += dp[k]/2
                    ndp[k-1] += dp[k]/2

        dp = ndp

    res += dp[0] * R[i] * 1/2 * A[i]
    ndp = [0 for j in range(N+1)]
    for k in range(N+1):
        if not k:
            ndp[0] += dp[0]/2
        else:
            ndp[k] += dp[k]/2
            ndp[k-1] += dp[k]/2
    dp = ndp


    for j in range(i+1,N):
        ndp = [0 for k in range(N+1)]
        if A[j] >= A[i]:
            res += dp[0] * R[j] * 1/2 * A[i]
        for k in range(N+1):
            if not dp[k]:
                continue

            if A[j] < A[i]:
                ndp[k+1] += dp[k]/2
                ndp[k] += dp[k]/2
            else:
                if not k:
                    ndp[k] += dp[k]/2
                else:
                    ndp[k] += dp[k]/2
                    ndp[k-1] += dp[k]/2
        dp = ndp

    #print(res,dp)

print(res)