n,m = map(int,input().split())
apo = []
hotel = []

for i in range(m):
    ap = input().split()
    ap = [ap[0]] + ap[1].split(":") + [ap[2]] + ap[3].split(":")
    ci = int(ap[0])*1440 + int(ap[1])*60 + int(ap[2])
    co = int(ap[3])*1440 + int(ap[4])*60 + int(ap[5])
    apo.append([ci,co])

apo.sort()
cnt = 0
for i in range(m):
    hotel.append(apo[i][1])
    len_h = len(hotel)
    for j in range(len_h-1,-1,-1):
        if hotel[j]<apo[i][0]:
            del hotel[j]
            cnt+=1
    if len(hotel)>n:
        hotel.sort()
        del hotel[-1]
cnt += len(hotel)
print(cnt)