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
def I(): return int(sys.stdin.readline().rstrip())
def LI(): return list(map(int,sys.stdin.readline().rstrip().split()))  #空白あり


N = I()
t = LI()
v = LI()

max_v = [0]*(N+1)  # 0秒後,t1秒後,t1+t2秒後,…の時点で出せる最大速度
for i in range(N-1):
    max_v[i+1] = min(v[i],v[i+1],max_v[i]+t[i])
for i in range(N-2,-1,-1):
    max_v[i+1] = min(max_v[i+1],v[i],v[i+1],max_v[i+2]+t[i+1])

ans = 0
for i in range(N):
    if t[i] >= (v[i]-max_v[i]) + (v[i]-max_v[i+1]):
        ans += t[i]*v[i]-(v[i]-max_v[i])**2/2-(v[i]-max_v[i+1])**2/2
    else:
        x = (t[i]+max_v[i]+max_v[i+1])/2
        ans += t[i]*x-(x-max_v[i])**2/2-(x-max_v[i+1])**2/2

print(ans)