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 math
  import collections
  N = int(input())
  A = [int(input()) for x in range(N)]
  c = collections.Counter(A)
  #print(c)
  aaa = []
  for i in (reversed(sorted(A))):
      #print(i)
      #print(">>",c[i])
      #print()
      if c[i] > 1:
          c[i]-=2
          aaa.append(i)
      if len(aaa) == 2:
          break
  if len(aaa) < 2:
      print(0)
  else:
      print(aaa[0]*aaa[1])3
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"}]