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())
  A=[int(i) for i in input().split()]
  A.sort()
  lis=[]
  dic={}
  for i in range(N):
  	try:
        dic[A[N-i-1]]=dic[A[N-i-1]]+1
        if dic[A[N-i-1]]%2==0:
          lis+=[A[N-i-1]]
      except:
        dict.setdefault(A[N-i-1],1)
      if len(lis)==2:
        break
  if len(lis)<2:print(0)
  else:print(lis[0]*lis[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"}]