Problem: In the year 2168, AtCoder Inc., which is much larger than now, is starting a limited express train service called AtCoder Express.

In the plan developed by the president Takahashi, the trains will run as follows:

* A train will run for (t_1 + t_2 + t_3 + ... + t_N) seconds.
* In the first t_1 seconds, a train must run at a speed of at most v_1 m/s (meters per second). Similarly, in the subsequent t_2 seconds, a train must run at a speed of at most v_2 m/s, and so on.



According to the specifications of the trains, the acceleration of a train must be always within ±1m/s^2. Additionally, a train must stop at the beginning and the end of the run.

Find the maximum possible distance that a train can cover in the run.

Constraints

* 1 \leq N \leq 100
* 1 \leq t_i \leq 200
* 1 \leq v_i \leq 100
* All input values are integers.

Input

Input is given from Standard Input in the following format:


N
t_1 t_2 t_3 … t_N
v_1 v_2 v_3 … v_N


Output

Print the maximum possible that a train can cover in the run.
Output is considered correct if its absolute difference from the judge's output is at most 10^{-3}.

Examples

Input

1
100
30


Output

2100.000000000000000


Input

2
60 50
34 38


Output

2632.000000000000000


Input

3
12 14 2
6 2 7


Output

76.000000000000000


Input

1
9
10


Output

20.250000000000000000


Input

10
64 55 27 35 76 119 7 18 49 100
29 19 31 39 27 48 41 87 55 70


Output

20291.000000000000

Solution (in PYTHON3):

Solution:
def main():
    N = int(input())
    Tn = tuple(map(int, input().split()))
    Vn = tuple(map(int, input().split()))

    t = (0,) + Tn + (0,)
    v = (0,) + Vn + (0,)
    maxv = [0]
    for i in range(1, N + 1):
        if v[i-1] <= v[i] > v[i+1]:
            maxv += [v[i]] * (t[i] * 2 - 1)
        elif v[i-1] > v[i] <= v[i+1]:
            maxv += [v[i]] * (t[i] * 2 + 1)
        else:
            maxv += [v[i]] * t[i] * 2
    maxv += [0]

    cnt = len(maxv)
    for i in range(1, cnt):
        maxv[i] = min(maxv[i], maxv[i-1] + 0.5)

    for i in range(cnt - 2, -1, -1):
        maxv[i] = min(maxv[i], maxv[i+1] + 0.5)

    s = 0
    for i in range(cnt - 1):
        s += (maxv[i] + maxv[i+1]) * 0.5 / 2
    print(s)

main()