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: 10
  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
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."}]