D. Delivery Forces
time limit per test
2 seconds
memory limit per test
512 megabytes
input
standard input
output
standard output

Gry finally becomes the Executive Courier Officer in "Universe Express". He has $$$n$$$ subordinate couriers with some delivery strength $$$f_i$$$. The delivery strength of a team of three people is the median of their strength, i.e., the middle element after the sorting. Please help Gry to split the couriers into $$$k$$$ teams of three people in order to maximize the total delivery strength of "Universe Express". The total strength is the sum of the strength of these $$$k$$$ teams.

Input
  • One line containing the number of couriers in the company, $$$n$$$ ($$$1 \leq n \leq 10^6$$$), where $$$n$$$ is a multiple of $$$3$$$.
  • One line containing the strengths of the $$$n$$$ couriers $$$f_1$$$...$$$f_n$$$ ($$$1 \le f \le 10^6$$$).
Output

The sole line of the output should contain the maximal strength of "Universe Express".

Examples
Input
3
1 2 3
Output
2
Input
6
5 6 2 3 1 4
Output
8