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 = [int(a) for a in input().split()]
  
  dic = {}
  for a in A:
    dic[a] = dic.get(a,0) + 1
  
  2p = []
  ans = 0
  
  for k in dic:
    if dic[k] >= 4:
      ans = max(ans,dic[k]**2)
    elif dic[k] >= 2:
      2p.append(dic[k])
  if len(2p)>=2:
    2p.sort(reverse=True)
    ans = max(ans,2p[0]*2p[1])
  print(ans)
  
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"}]