The Fair Nut and Elevator

题意翻译

有一栋楼里有一个电梯，这个电梯一次只能送一个人，且他每送完一个人到达他想要到达的楼层时就一定要回到电梯原来的楼层。现在这栋楼中第i层有a${_i}$个人，每天早上每个人都要到一楼（本来就在一楼的电梯也要下去再上来），之后傍晚每个人都要从一楼去他们住的地方，请问电梯每天需要走的最少层数

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.

输入输出格式

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

输入样例 #1

3
0 2 1

输出样例 #1

16

输入样例 #2

2
1 1

输出样例 #2

4

说明

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.