def solve(n, m, guestdata):
    schedulenote = {(d,h,m) : 0
                for d in range(2, 9)
                for h in range(0, 24)
                for m in range(0, 60)}
    schedulelist = [(d,h,m)
                for d in range(2, 9)
                for h in range(0, 24)
                for m in range(0, 60)]
    totalcount = 0
    guestdata.sort(key=lambda x: x.split(" ")[2:])

    for guest in guestdata:
        d = guest.split(" ")
        checkin_day = int(d[0])
        checkin_h = int(d[1][:2])
        checkin_m = int(d[1][3:])
        checkout_day = int(d[2])
        checkout_h = int(d[3][:2])
        checkout_m = int(d[3][3:])

        checkin = (checkin_day, checkin_h, checkin_m)
        checkout = (checkout_day, checkout_h, checkout_m)
        available = True

        target_schedule = schedulelist[schedulelist.index(checkin):schedulelist.index(checkout) + 1]

        for schedule in target_schedule:
            if schedulenote[schedule] >= n:
                available = False
                break

        if available:
            totalcount += 1
            for schedule in target_schedule:
                schedulenote[schedule] += 1

    return totalcount

if __name__ == "__main__":
    l = input().split(" ")
    n, m = int(l[0]), int(l[1])
    data = [input() for _ in range(0, m)]
    print(solve(n, m, data))