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: def resolve():
  	n=int(input())
  	a=list(map(int,input().split()))
  	s=list(set(a))[::-1]
  	l=[0]*3
  	k=0
  	for i in s:
  		if a.count(i)>=4:
  			l[k],l[k+1]=i,i
  			k+=2
  		elif a.count(i)>=2:
  			l[k]=i
  			k+=1
  		if k>1:
  			break
  	print(l[0]*l[1])
  resolve():
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"}]