import sys
input = sys.stdin.readline

def f(d, hm):
    d = int(d)
    h, m = map(int, hm.split(":"))
    return d * 1440 + h * 60 + m

N, M = map(int, input().split())
D = []
for i in range(M):
    d1, hm1, d2, hm2 = input().split()
    D.append((f(d2, hm2), f(d1, hm1)))
    
D.sort()
ans = 0
now = [-1] * N
for r, l in D:
    ind = -1
    maxv = -10
    for i in range(N):
        if now[i] < l and now[i] > maxv:
            ind = i
            maxv = now[i]
    if ind == -1:
        continue
    ans += 1
    now[ind] = r
    
print(ans)