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:
import sys
input = sys.stdin.readline

def main():
    N = int(input())
    t = list(map(lambda x: int(x) * 2, input().split()))
    v = list(map(float, input().split())) + [0]

    for i in range(1, N):
        t[i] += t[i-1]
    t += [t[-1]]
    vnow = [0.0] * (t[-1] + 1)
    vr = [0.0] * (t[-1] + 1)
    r = 0
    for i in range(1, len(vr)):
        if i < t[r]:
            vr[i] = v[r]
        elif i == t[r]:
            vr[i] = min(v[r], v[r+1])
            r += 1
        vnow[i] = min(vnow[i-1] + 0.5, vr[i])
    for i in range(len(vr)-2, -1, -1):
        vnow[i] = min(vnow[i], vnow[i+1] + 0.5)
    
    print(sum(vnow) / 2)

if __name__ == "__main__":
    main()