Problem:
﻿Score : 400 points

Problem Statement

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}.

Sample Input 1

1
100
30

Sample Output 1

2100.000000000000000

The maximum distance is achieved when a train runs as follows:

In the first 30 seconds, it accelerates at a rate of 1m/s^2, covering 450 meters.

In the subsequent 40 seconds, it maintains the velocity of 30m/s, covering 1200 meters.

In the last 30 seconds, it decelerates at the acceleration of -1m/s^2, covering 450 meters.

The total distance covered is 450 + 1200 + 450 = 2100 meters.

Sample Input 2

2
60 50
34 38

Sample Output 2

2632.000000000000000

The maximum distance is achieved when a train runs as follows:

In the first 34 seconds, it accelerates at a rate of 1m/s^2, covering 578 meters.

In the subsequent 26 seconds, it maintains the velocity of 34m/s, covering 884 meters.

In the subsequent 4 seconds, it accelerates at a rate of 1m/s^2, covering 144 meters.

In the subsequent 8 seconds, it maintains the velocity of 38m/s, covering 304 meters.

In the last 38 seconds, it decelerates at the acceleration of -1m/s^2, covering 722 meters.

The total distance covered is 578 + 884 + 144 + 304 + 722 = 2632 meters.

Sample Input 3

3
12 14 2
6 2 7

Sample Output 3

76.000000000000000

The maximum distance is achieved when a train runs as follows:

In the first 6 seconds, it accelerates at a rate of 1m/s^2, covering 18 meters.

In the subsequent 2 seconds, it maintains the velocity of 6m/s, covering 12 meters.

In the subsequent 4 seconds, it decelerates at the acceleration of -1m/s^2, covering 16 meters.

In the subsequent 14 seconds, it maintains the velocity of 2m/s, covering 28 meters.

In the last 2 seconds, it decelerates at the acceleration of -1m/s^2, covering 2 meters.

The total distance covered is 18 + 12 + 16 + 28 + 2 = 76 meters.

Sample Input 4

1
9
10

Sample Output 4

20.250000000000000000

The maximum distance is achieved when a train runs as follows:

In the first 4.5 seconds, it accelerates at a rate of 1m/s^2, covering 10.125 meters.

In the last 4.5 seconds, it decelerates at the acceleration of -1m/s^2, covering 10.125 meters.

The total distance covered is 10.125 + 10.125 = 20.25 meters.

Sample Input 5

10
64 55 27 35 76 119 7 18 49 100
29 19 31 39 27 48 41 87 55 70

Sample Output 5

20291.000000000000

Solution in Python (3.4.3) (judge verdict: Wrong Answer)

n=int(input())
t=[int(i) for i in input().split()]
v=[int(i) for i in input().split()]
S=[0 for i in range(n)]
S1=[0 for i in range(n)]
S2=[0 for i in range(n)]
vel=[0 for i in range(n)]

dt=[0 for i in range(n)]
v0=[0 for i in range(n)]
ve=[0 for i in range(n)]

for i in range(n):
    if n ==1:
        dt[0]=t[0]
    elif i==n-1:
        v0[i]=ve[i-1]
        ve[i]=0
        dt[i]=t[i]
    else:
        v0[i]=ve[i-1]
        ve[i]=min(v[i+1],v[i])
        dt[i]=t[i]
"""
print(dt)
print(v0)
print(ve)
print(v)
"""

for i in range(n):

    ttt=0.5*(ve[i]+dt[i]-v0[i])
    vvv=ttt+v0[i]
    if vvv-v[i]>=0:
        S[i]=0.5*(v0[i]+vvv)*ttt + 0.5*(ve[i]+vvv)*(dt[i]-ttt) - (ttt-v[i]+v0[i])*(vvv-v[i]) 
        S1[i]=0.5*(v0[i]+vvv)*ttt + 0.5*(ve[i]+vvv)*(dt[i]-ttt)
        S2[i]=(ttt-v[i]+v0[i])*(vvv-v[i]) 
    else:
        S[i]=0.5*(v0[i]+vvv)*ttt + 0.5*(ve[i]+vvv)*(dt[i]-ttt)
        S1[i]=0.5*(v0[i]+vvv)*ttt + 0.5*(ve[i]+vvv)*(dt[i]-ttt)
        S2[i]=0

print(sum(S))