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: import collections
  
  n = int(input())
  A = list(map(int, input().split()))
  a = collections.Counter(A)
  firstnum = 0
  secondnum = 0
  firstl = 0
  secondl = 0
  values, counts = zip(*a.most_common())
  if len(values) == 1 and counts[0] >= 4:
      print(values[0] ** 2)
  else:
      for i, j in a.items():
          if i >= firstl and j >= 2:
              secondnum = firstnum
              firstnum = j
              secondl = firstl
              firstl = i
          elif secondl <= i < firstl and j >= 2:
              secondnum = j
              secondl = i
      print(firstl * secondl)
  
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"}]