class A
  def initialize
    n = gets.chomp.to_i

    items = Array.new(11, 0)

    n.times do
      list = gets.chomp.split(' ').map(&:to_i)

      list.each do |id|
        items[id] += 1
      end
    end

    answer = 0
    sub = 0

    items.each do |num|
      answer += num/2
      sub += num%2
    end

    puts answer + sub/4
  end
end

A.new