N,M=map(int,input().split())

list1=[]
list2=[0 for i in range(N)]
for i in range(M):
    a=input()
    a=a.rstrip().split(" ")
    a[1]=a[1].split(":")
    a[3]=a[3].split(":")
    list1.append([int(a[3][1])+int(a[3][0])*60+int(a[2])*60*24,int(a[1][1])+int(a[1][0])*60+int(a[0])*60*24])
list1.sort()
#print(list1)
cnt=0
for j in range(M):
    
    for k in range(N):
        if list2[k]<list1[j][1]:
            list2[k]=list1[j][0]
            cnt+=1
            list2.sort(reverse=True)
            list1[j][1]=0
print(cnt)