import sys

# sys.setrecursionlimit(200005)
# sys.set_int_max_str_digits(200005)
int1 = lambda x: int(x)-1
pDB = lambda *x: print(*x, end="\n", file=sys.stderr)
p2D = lambda x: print(*x, sep="\n", end="\n\n", file=sys.stderr)
def II(): return int(sys.stdin.readline())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LLI1(rows_number): return [LI1() for _ in range(rows_number)]
def SI(): return sys.stdin.readline().rstrip()

dij = [(0, 1), (-1, 0), (0, -1), (1, 0)]
# dij = [(0, 1), (-1, 0), (0, -1), (1, 0), (1, 1), (1, -1), (-1, 1), (-1, -1)]
# inf = -1-(-1 << 31)
inf = -1-(-1 << 62)

# md = 10**9+7
md = 998244353

n = II()
a = LI()
r = LI()

ans = 0
for i in range(n):
    dp = [1]
    for j in range(i):
        if a[j] <= a[i]: dp.insert(0, 0)
        m = len(dp)
        pre, dp = dp, [0]*m
        for k in range(1, m):
            pre[k] *= 0.5
            dp[k] += pre[k]
            dp[k-1] += pre[k]
        dp[0]+=pre[0]
    for j in range(i, n):
        if a[j] < a[i]: dp.insert(0, 0)
        ans += dp[0]*a[i]*r[j]*0.5
        m = len(dp)
        pre, dp = dp, [0]*m
        for k in range(m):
            dp[k] = pre[k]*0.5
            if k+1 < m: dp[k] += pre[k+1]*0.5
        # print(i,j,dp)
print(ans)