n = int(input())
*a, = map(int,input().split())
*r, = map(int,input().split())

ans = 0.0
for i,ai in enumerate(a):
    p = [1.0]
    L = 1
    for j,aj in enumerate(a):
        for k in range(L):
            p[k] /= 2
        
        if aj < ai or (aj==ai and j < i):
            p.append(0.0)
            L += 1
            for k in range(1,L)[::-1]:
                p[k] += p[k-1]
        else:
            if j >= i:
                ans += r[j]*ai*p[0]
            else:
                p[0] *= 2
            
            for k in range(L-1):
                p[k] += p[k+1]

print(ans)