CF1084A.The Fair Nut and Elevator

普及/提高-

通过率：0%

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题目描述

The Fair Nut lives in $n$ story house. $a_i$ people live on the $i$ -th floor of the house. Every person uses elevator twice a day: to get from the floor where he/she lives to the ground (first) floor and to get from the first floor to the floor where he/she lives, when he/she comes back home in the evening.

It was decided that elevator, when it is not used, will stay on the $x$ -th floor, but $x$ hasn't been chosen yet. When a person needs to get from floor $a$ to floor $b$ , elevator follows the simple algorithm:

Moves from the $x$ -th floor (initially it stays on the $x$ -th floor) to the $a$ -th and takes the passenger.
Moves from the $a$ -th floor to the $b$ -th floor and lets out the passenger (if $a$ equals $b$ , elevator just opens and closes the doors, but still comes to the floor from the $x$ -th floor).
Moves from the $b$ -th floor back to the $x$ -th.

The elevator never transposes more than one person and always goes back to the floor $x$ before transposing a next passenger. The elevator spends one unit of electricity to move between neighboring floors. So moving from the $a$ -th floor to the $b$ -th floor requires $|a - b|$ units of electricity.Your task is to help Nut to find the minimum number of electricity units, that it would be enough for one day, by choosing an optimal the $x$ -th floor. Don't forget than elevator initially stays on the $x$ -th floor.

输入格式

The first line contains one integer $n$ ( $1 \leq n \leq 100$ ) — the number of floors.

The second line contains $n$ integers $a_1, a_2, \ldots, a_n$ ( $0 \leq a_i \leq 100$ ) — the number of people on each floor.

输出格式

In a single line, print the answer to the problem — the minimum number of electricity units.

输入输出样例

输入#1
```
3
0 2 1
```
输出#1
```
16
```
输入#2
```
2
1 1
```
输出#2
```
4
```

说明/提示

In the first example, the answer can be achieved by choosing the second floor as the $x$ -th floor. Each person from the second floor (there are two of them) would spend $4$ units of electricity per day ( $2$ to get down and $2$ to get up), and one person from the third would spend $8$ units of electricity per day ( $4$ to get down and $4$ to get up). $4 \cdot 2 + 8 \cdot 1 = 16$ .

In the second example, the answer can be achieved by choosing the first floor as the $x$ -th floor.

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