import sequtils,algorithm,sugar
proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0' or k > '9': break
    result = 10 * result + k.ord - '0'.ord
proc parseLine(): tuple[x,y:int] =
  result.x = scan() * 1440 + scan() * 60 + scan()
  result.y = scan() * 1440 + scan() * 60 + scan()

let n = scan()
let m = scan()
let U = newSeqWith(m,parseLine()).sortedByIt(it.y)
var preY = newSeq[int](n)
var ans = 0
for u in U: # preY は 小さい順に並んでいると過程
  let i = preY.lowerBound(u.x) # それ以上の初のindex
  if i == 0: continue
  if preY[i-1] >= u.x : continue
  preY[i-1] = u.y
  ans += 1
  preY.sort(cmp)
echo ans