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

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

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