module MakePairs
  def solve(ct)
    ct.map{|x| x / 2}.sum
  end

  module_function :solve
end

n = gets.chomp.to_i
ct = Array.new(n + 1, 0)

gets.chomp.split(/\s+/).map(&:to_i).each do |i|
  ct[i] += 1
end
  
puts MakePairs.solve(ct)