output_description: Print the maximum possible area of the rectangle. If no rectangle can be
  formed, print 0.
  
  * * *
input_description: Input is given from Standard Input in the following format:
  
      
      
      N
      A_1 A_2 ... A_N
attempt: from sys import stdin
  input = stdin.readline
  
  def main():
      n = int(input())
      a = list(map(int, input().split()))
  
      if 4 <= n and n <= 10**5:
          
          for i in a:
              if not (1 <= i and i <= 10**9 and type(i) == int:
                  return
  
          j = [x for x in a if a.count(x) > 1]
          j.sort(reverse = True)
  
          if len(j) < 4:
              print(0)
              return
  
          print(j[0]*j[2])
  
  if __name__ == "__main__":
      main()
problem_description: Statement
  
  We have N sticks with negligible thickness. The length of the i-th stick is
  A_i.
  
  Snuke wants to select four different sticks from these sticks and form a
  rectangle (including a square), using the sticks as its sides. Find the
  maximum possible area of the rectangle.
samples: [{"input": "6\n    3 1 2 4 2 1", "output": "2\n    \n\n1 \\times 2 rectangle can be formed.\n\n* * *"}, {"input": "4\n    1 2 3 4", "output": "0\n    \n\nNo rectangle can be formed.\n\n* * *"}, {"input": "10\n    3 3 3 3 4 4 4 5 5 5", "output": "20"}]