list = Array.new
power_up = 0
gets.chomp.to_i.times { gets.chomp.split.map(&:to_i).each{ |i| list << i } }
list.uniq.each do |i|
	power_up += list.count(i) / 2
	list.delete(i) if list.count(i).even?
end
puts power_up + list.uniq.length / 4