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())
  l = map(int, input().split())
  c = collections.Counter(l)
  c = sorted(c.items(), key=lambda c:c[0], reverse=True)
  
  ans = 1
  cnt = 0
  
  for key,val in c:
    if cnt=0 and val>=4:
      ans=key**2
      break
    if val>=2:
      ans*=key
      cnt+=1
    if cnt == 2:
      break
  else:
    ans = 0
  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"}]