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 = input()
  A = list(map(int, input().split()))
  A.sort(reverse=True)
  
  now = A[0]
  tateyoko = [0, 0]
  count = 0
  nowflag = False
  for i in range(1, N):
    if (A[i] == now) and !nowflag:
      tateyoko[count] = now
      count += 1
      nowflag = True
    else:
      nowflag = False
    if count == 2:
      break
    now = A[i]
    
  print(tateyoko[0] * tateyoko[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"}]