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
n = int(input())
t = list(map(int, input().split()))
v = list(map(int, input().split()))
v.append(0)

# forward
now = 0
for i in range(n):
    if now + t[i] < v[i]:
        v[i] = now + t[i]

    if v[i] <= v[i+1]:
        now = v[i]
    elif t[i] + v[i+1] + now < 2 * v[i]:
        v[i] = (t[i] + v[i+1] + now) / 2
        now = v[i+1]
    else:
        now = v[i+1]

# back
now = 0
for i in range(n-1, -1, -1):
    if now + t[i] < v[i]:
        v[i] = now + t[i]

    if v[i] <= v[i-1]:
        now = v[i]
    elif t[i] + v[i-1] + now < 2 * v[i]:
        v[i] = (t[i] + v[i-1] + now) / 2
        now = v[i-1]
    else:
        now = v[i-1]

ans = 0
now = 0
for i in range(n):
    t1 = v[i] - now
    t3 = v[i] - v[i+1]
    t2 = t[i] - t1 - t3
    ans += now * t1 + t1 * t1 / 2
    now = v[i] # now += t1
    ans += now * t2
    # now = now
    ans += now * t3 - t3 * t3 / 2
    now -= t3

print(ans)