output_description: Print the answer.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      a_1 a_2 ... a_{3N}
attempt: #!/usr/bin/env python3
  from collections import defaultdict,deque
  from heapq import heappush, heappop
  from bisect import bisect_left, bisect_right
  import sys, random, itertools, math
  sys.setrecursionlimit(10**5)
  input = sys.stdin.readline
  sqrt = math.sqrt
  def LI(): return list(map(int, input().split()))
  def LF(): return list(map(float, input().split()))
  def LI_(): return list(map(lambda x: int(x)-1, input().split()))
  def II(): return int(input())
  def IF(): return float(input())
  def LS(): return list(map(list, input().split()))
  def S(): return list(input().rstrip())
  def IR(n): return [II() for _ in range(n)]
  def LIR(n): return [LI() for _ in range(n)]
  def FR(n): return [IF() for _ in range(n)]
  def LFR(n): return [LI() for _ in range(n)]
  def LIR_(n): return [LI_() for _ in range(n)]
  def SR(n): return [S() for _ in range(n)]
  def LSR(n): return [LS() for _ in range(n)]
  mod = 1000000007
  inf = 1e10
  
  #solve
  def solve():
      n = II()
      a = LI()
      a.sort(
      print(sum[n::2])
      return
  
  
  #main
  if __name__ == '__main__':
      solve()
  
problem_description: Statement
  
  There are 3N participants in _AtCoder Group Contest_. The _strength_ of the
  i-th participant is represented by an integer a_i. They will form N teams,
  each consisting of three participants. No participant may belong to multiple
  teams.
  
  The strength of a team is defined as the second largest strength among its
  members. For example, a team of participants of strength 1, 5, 2 has a
  strength 2, and a team of three participants of strength 3, 2, 3 has a
  strength 3.
  
  Find the maximum possible sum of the strengths of N teams.
samples: [{"input": "2\n    5 2 8 5 1 5", "output": "10\n    \n\nThe following is one formation of teams that maximizes the sum of the\nstrengths of teams:\n\n  * Team 1: consists of the first, fourth and fifth participants.\n  * Team 2: consists of the second, third and sixth participants.\n\n* * *"}, {"input": "10\n    1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000 1000000000", "output": "10000000000\n    \n\nThe sum of the strengths can be quite large."}]