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: a = int(input())
  ar = list(map(int,input().split(" ")))
  br = sorted(set(ar))
  cr = []
  for b in br:
      if ar.count(b) >= 2:
          cr.append(b)
  if len(cr) == 0:
      print(0)
  else:
  	if ar.count(max(cr)) >= 4:
      	print(max(cr) ** 2)
  	else:
      	dr = sorted(cr,reverse=True)
      	print(dr[0] * dr[1])
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"}]