n = gets.chomp.to_i
items = Hash.new(0)
n.times do
  gets.chomp.split(" ").map(&:to_i).each do |i|
    items[i] += 1
  end
end
pu = 0
pu1 = 0
items.each do |k, v|
  if v >= 2 then
    p = v / 2
    pu += p
    items[k] -= 2 * p
    pu1 += items[k]
  else
    pu1 += v
  end
end
puts pu + pu1/4