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: #Make a Rectangle
  N = int(input())
  A = list(map(int, input().split())
  
  a = sorted(A, reverse=True)
  b = []
  
  i = 0
  while i<N-2:
      if ( a[i]==a[i+1] ):
          b+=[a[i]]
          i+=2
      else:
          i+=1
      if (len(b)>=2):
          break
  
  if (len(b)<2):
      print(0)
  else:
      print(b[0]*b[1])
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"}]