class Calc0029
  def initialize(args)
    args = args.map { |l| l.chomp.split(/\s+/) }
    @n = args.shift.first.to_i
    @items = args.map { |l| l.map(&:to_i) }
  end

  def run
    is = @items.flatten.group_by(&:itself).map { |no, g| g.size }
    is.map { |i| i / 2 }.inject(:+) +
    is.select { |i| i % 2 == 1 }.size / 4
  end
end

puts Calc0029.new(STDIN.readlines).run if __FILE__ == $0