items = Hash.new(0)
gets.to_i.times do
  gets.split.map(&:to_i).each do |i|
    items[i] += 1
  end
end
count = 0
items.each do |key, i|
  count += i/2
  items[key] = i % 2
end
count += items.values.inject(:+)/4
puts count