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()))

Tsum = sum(T)
keika = []
tmp = 0
for i in range(N):
    keika.append([tmp,tmp+T[i]])
    tmp += T[i]

G = [[0]*(N+1) for i in range(2*Tsum+1)]

for i in range(2*Tsum+1):
    G[i][0] = min(i/2,Tsum-i/2)
for i in range(N):
    t0,t1 = keika[i]
    for j in range(2*t0):
        G[j][i+1] = V[i] + t0 - j/2
    for j in range(2*t0,2*t1+1):
        G[j][i+1] = V[i]
    for j in range(2*t1+1,2*Tsum+1):
        G[j][i+1] = V[i] + j/2 - t1

ans = 0
for i in range(2*Tsum):
    v0 = min(G[i])
    v1 = min(G[i+1])
    ans += (v0+v1)/4
print(ans)