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()))

T = [0 for i in range(n)]
T[0] = t[0]
for i in range(n-1):
    T[i+1] = T[i] + t[i+1]

INF = float('inf')
V = [INF for i in range(2*T[n-1]+1)]

for i in range(2*T[n-1]+1):
    V[i] = min(V[i], 0.5 * i)
    V[i] = min(V[i], T[n-1] - 0.5 * i)

for vi in range(n):
    for ti in range(2*T[n-1]+1):
        if vi == 0:
            if ti <= T[0] * 2:
                V[ti] = min(V[ti], v[0])
            else:
                V[ti] = min(V[ti], v[0] + ti * 0.5 - T[0])
        else:
            if ti <= T[vi-1] * 2:
                V[ti] = min(V[ti], v[vi] + T[vi-1] - ti * 0.5)
            elif (T[vi-1] * 2 <= ti) and (ti <= T[vi] * 2):
                V[ti] = min(V[ti], v[vi])
            else:
                V[ti] = min(V[ti], v[vi] + (ti * 0.5 - T[vi]))

ans = 0
for i in range(2*T[n-1]):
    ans += (V[i] + V[i+1]) * 0.5 * 0.5

print(ans)