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: N = int(input())
  A = list(map(int, input().split()))
  
  bar_length_count = dict()
  for a in A:
      bar_length_count[a] = bar_length_count.get(a, 0) + 1
  
  for val in bar_length_count.values():
      pass
  
  count_at_least_2 = 0
  for val in bar_length_count.values():
      if val >= 2:
          if val >= 4:
              count_at_least_2 += 2
          else:
              count_at_least_2 += 1
  
  if count_at_least_2 < 2:
      import sys
      print(0)
      sys.exit(0)
  
  else:
      bar_length_count = sorted([(k, v) for bar_length_count.items() if v >= 2], reverse=True)
      if bar_length_count[0][1] >= 4:
          print(bar_length_count[0][0]**2)
      else:
          print(bar_length_count[0][0]*bar_length_count[1][0])
          
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"}]