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 Counter
  
  n = int(input())
  a = list(map(int,input().split()))
  
  ac = Counter(a)
  
  cur_a = 0
  cur_c = 0
  res = 0
  for a,c in ac.items():
  	if c < 2:
  		break
  	if c >= 4:
  		res = max(res,a*a)
  	if cur_c == c
  		res = max(res,cur_a*a)
  		cur_a = max(cur_a,a)
  	else:
  		cur_a = a
  		cur_c = c
  
  print(res)
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"}]