+ محدودیت زمان: ۱ ثانیه + محدودیت حافظه: ۳۲ مگابایت ---------- 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 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 well-intentioned 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. # Input The first line of input contains the integer N, the number of books the customer bought. The second line contains N integer $C_i$ , the price of each book. # Output The first and only line of output must contain the required minimal price. # Constraints * $1 \leq N \leq 10^5 $ * $1 \leq C_i \leq 10^5 $ # Sample test data ## input 1 ``` 4 4 2 3 1 ``` ## output 1 ``` 8 ``` ## input 2 ``` 6 4 5 4 3 4 2 ``` ## output 2 ``` 16 ```