h = Hash.new(0)
n = gets.chomp.to_i
n.times do
  gets.split.map(&:to_i).each do |i|
    h[i+1] += 1
  end
end

count = 0
rest = 0
(n * 3).times do |i|
  count += h[i] / 2
  rest += 1 if h[i] % 2 == 1
end

count += rest/4
puts count