\(1^{st}\) round, October \(17^{th}\), 2015

There is a promotional offer in a bookstore “Take 3, pay for the 2 more expensive ones”. So, each
customer who picks 3 books gets the cheapest one for free. Of course, the customer can take even
more books and, depending on the way the books are arranged into groups of three, get the cheapest
one in each group for free.

For example, let the prices of the books taken by the customer be: 10 3 2 4 6 4 9. If he arranges them
into groups: (10, 3, 2), (4, 6, 4) and (9), he will get the books priced 2 from the first group for free and
the book priced 4 from the second group. We can see that he won’t get anything for free from the third
group because it contains only one book.

The lady working in the bookstore is we\(ll-in\)tentioned and she always wants to lower the price for each
customer as much as possible. For given book prices, help the lady arrange the books into groups in
the best way possible, so that the total price the customer has to pay is minimal.

Please note: The lady doesn’t have to arrange the books into groups so that each group contains
exactly 3 books, but the number of books in a group needs to be between 1 and 3, inclusively.

In test cases worth 50% of points, it will hold that \(N \le 2000\).

The first line of input contains the integer N (\(1 \le N \le 100\,000\)), the number of books the customer
bought.
Each of the following N lines contains a single integer Ci (\(1 \le Ci \le 100\,000\)), the price of each book.

The first and only line of output must contain the required minimal price.

생성자가 기록되지 않았습니다.

출처 COCI 2015/2016 Contest 1