n = gets.to_i
items = n.times.map { gets.split.map(&:to_i)}.flatten.sort
counts = (1..10).map{|i|
    count = items.count(i)
    count.divmod(2)
}
puts counts.inject(0) {|s,v| s + v[0]} + counts.inject(0) {|s,v| s + v[1] }.div(4)