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
import sys
input = sys.stdin.readline

N = int(input())
T0 = list(map(int, input().split()))
V = list(map(int, input().split()))

INF = 1000
def main():
    Tmax = 0
    T = [0]
    for t in T0:
        Tmax += t
        T.append(Tmax)

    preh = 0
    ans = 0
    for t0 in range(2*Tmax+1):
        t = t0/2
        height = INF
        for n in range(-1, N+1):
            if n == -1:
                t1, t2, v = -1, 0, 0
            elif n == N:
                t1, t2, v = Tmax, Tmax+1, 0
            else:
                t1, t2, v = T[n], T[n+1], V[n]
            
            if t < t1:
                y = v + t1 - t
            elif t1 <= t <= t2:
                y = v
            else:
                y = v + t - t2
            height = min(height, y)
        
        ans += (preh + height)*0.5/2
        preh = height
    print(ans)

if __name__ == "__main__":
    main()