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 sys import stdin
  from itertools import groupby
  
  n = int(stdin.readline().rstrip())
  li = list(map(int, stdin.readline().rstrip().split()))
  
  li.sort(reverse=True)
  lin = []
  for key, value in groupby(li):
      lin.append((key, len(list(value))))
  
  mae = 0
  ato = 0
  for i in lin:
      if i[1] >= 2 and mae == 0:
          mae = i[0]
      elif i[1] >= 2 and ato == 0:
          ato = i[0]
  
  print(mae * ato)
  
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"}]