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:
def solve():
  n=int(input())
  arr1=list(map(int,input().split()))
  arr2=list(map(int,input().split()))
  tlist=[0]
  for val in arr1:
    tlist.append(tlist[-1]+val)
  t=tlist[-1]
  ans=0
  for i in range(1,2*t):
    tt=i/2
    tmp=10**18
    for j in range(n):
      if tt<=tlist[j]:
        tmp=min(tmp,arr2[j]+(tlist[j]-tt))
      elif tlist[j+1]<=tt:
        tmp=min(tmp,arr2[j]+(tt-tlist[j+1]))
      else:
        tmp=min(tmp,arr2[j])
    tmp=min(tmp,tt)
    tmp=min(tmp,t-tt)
    ans+=tmp
  print(ans/2)
solve()