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 collections import defaultdict
  N = int(input())
  A = sorted([int(i) for i in input().split()], reverse=True)
  A_dict = defaultdict(lambda:0)
  for a in A:
      A_dict[a] += 1
  key1 = 0
  key2 = 0
  for key in A_dict.keys():
      if key2 > 0:
          break
  
      if A_dict[key] > 3:
          if key1 == 0;
              key1 = key
          if key2 == 0;
              key2 = key
      elif A_dict[key] > 1:
          if key1 > 0:
              key2 = key
          else:
              key1 = key
  print(key1*key2)
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"}]