n = gets.to_i
items = n.times.each_with_object(Hash.new(0)) { |j,o|
    gets.chomp.split.map(&:to_i).each {|i|
        o[i] += 1
    }
}
dup_up = items.keys.inject(0) { |s,v|
    count = items[v]
    items[v] = count % 2
    s += count / 2
}
tetra_up = items.values.inject(0,&:+) / 4
puts dup_up + tetra_up