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:
#!/usr/bin/env python3
#ABC76 D

import sys
import math
import bisect
sys.setrecursionlimit(1000000000)
from heapq import heappush, heappop
from collections import defaultdict
from itertools import accumulate
from collections import Counter
from collections import deque
from operator import itemgetter
from itertools import permutations
mod = 10**9 + 7

n = int(input())
t = list(map(int,input().split()))
v = list(map(int,input().split()))

st = sum(t)
maxv = [0]
for i in range(n):
    maxv[-1] = min(maxv[-1],v[i])
    for _ in range(2*t[i]):
        maxv.append(v[i])
maxv[-1] = 0
for i in range(1,2*st+1):
    maxv[i] = min(maxv[i],maxv[i-1] + 0.5)
for i in range(2*st)[::-1]:
    maxv[i] = min(maxv[i],maxv[i+1] + 0.5)
ans = 0
for i in range(2*st):
    ans += (maxv[i] + maxv[i+1])*0.5 / 2
print(ans)