package main

import (
	"bufio"
	"fmt"
	"os"
	"sort"
	"strconv"
	"strings"
)

func configure(scanner *bufio.Scanner) {
	scanner.Split(bufio.ScanWords)
	scanner.Buffer(make([]byte, 1000005), 1000005)
}
func getNextString(scanner *bufio.Scanner) string {
	scanned := scanner.Scan()
	if !scanned {
		panic("scan failed")
	}
	return scanner.Text()
}
func getNextInt(scanner *bufio.Scanner) int {
	i, _ := strconv.Atoi(getNextString(scanner))
	return i
}
func getNextInt64(scanner *bufio.Scanner) int64 {
	i, _ := strconv.ParseInt(getNextString(scanner), 10, 64)
	return i
}
func getNextFloat64(scanner *bufio.Scanner) float64 {
	i, _ := strconv.ParseFloat(getNextString(scanner), 64)
	return i
}
func main() {
	fp := os.Stdin
	wfp := os.Stdout
	extra := 0
	if os.Getenv("I") == "IronMan" {
		fp, _ = os.Open(os.Getenv("END_GAME"))
		extra = 100
	}
	scanner := bufio.NewScanner(fp)
	configure(scanner)
	writer := bufio.NewWriter(wfp)
	defer func() {
		r := recover()
		if r != nil {
			fmt.Fprintln(writer, r)
		}
		writer.Flush()
	}()
	solve(scanner, writer)
	for i := 0; i < extra; i++ {
		fmt.Fprintln(writer, "-----------------------------------")
		solve(scanner, writer)
	}
}
func solve(scanner *bufio.Scanner, writer *bufio.Writer) {
	n := getNextInt(scanner)
	m := getNextInt(scanner)
	mm := make([]pair, m)
	for i := 0; i < m; i++ {
		mm[i][0] = datetominites(getNextInt(scanner), getNextString(scanner))
		mm[i][1] = datetominites(getNextInt(scanner), getNextString(scanner))
	}
	sort.Slice(mm, func(i, j int) bool {
		return mm[i][1] < mm[j][1]
	})
	var ans int
	q := make([]int, 0)
	for i := 0; i < m; i++ {
		for len(q) > 0 && q[0] < mm[i][0] {
			q = q[1:]
		}
		if len(q) < n {
			q = append(q, mm[i][1])
			ans++
		}
	}
	fmt.Fprintln(writer, ans)
}
func datetominites(d int, s string) int {
	hm := strings.Split(s, ":")
	return d*24*60 + strtoint(hm[0])*24 + strtoint(hm[1])
}
func strtoint(s string) int {
	return int(s[0]-'0')*10 + int(s[1]-'0')
}

type pair [2]int