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())
      vals = list(map(int, input().split()))
      d= {}
      s = [0, 0]
       
      for i in range(n):
          if(vals[i] in d.keys()):
              d[vals[i]] += 1
          else:
              d[vals[i]] = 1
       
       
      for i in d.keys():
          if(d[i] >= 4):
              s.append(i)
              s.append(i)
          elif(d[i] >= 2):
              s.append(i)
      s.sort()
       
      print(s[-1]*s[-2])
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"}]