A12187 | The Fair Nut and Elevator

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.

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.

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