class Powerup
    attr_reader :n, :abc

    def initialize(n: 0, abc: [])
        @n, @abc = n, abc
    end

    def cause
        begin
            @n = Integer(gets.chomp)
            @abc = @n.times.map { gets.chomp.split.map { |v| Integer(v) } }
        rescue
            
        end
    end

    def powerup_cnt(array)
        powerup = 0
        items = array.flatten.sort
        item_uniq = items.uniq
        item_uniq.each do |i|
            powerup += items.count(i)/2 if 2 <= items.count(i)
        end
        powerup += (items.size - (powerup*2)) / 4
        powerup
    end

    def result
        puts powerup_cnt(@abc)
    end

    def run
        cause
        result
    end
end

if $0 == __FILE__
    Powerup.new.run
end