N, M = gets.split.map(&:to_i)

DAY = 24 * 60

def to_time(str)
  h, m = str.split(':').map(&:to_i)
  h * 60 + m
end

reserve_list = []

M.times do
  d, t1, o, t2 = gets.chomp.split
  from = d.to_i * DAY + to_time(t1)
  to = o.to_i * DAY + to_time(t2)

  reserve_list << [from, to]
end

reserve_list.sort_by! { |f, t| t }
rooms = Array.new(N, -1)
ans = 0

reserve_list.each do |from, to|
  best_id = -1
  max_time = -Float::INFINITY

  N.times do |i|
    if rooms[i] < from && max_time < rooms[i]
      best_id = i
      max_time = rooms[i]
    end
  end

  if best_id != -1
    rooms[best_id] = to
    ans += 1
  end
end

puts ans