from bisect import bisect_left

n, m = map(int, input().split())
T = []
for _ in range(m):
    fd, ft, td, tt = input().split()
    fd = int(fd) - 1
    fh, fm = map(int, ft.split(':'))
    td = int(td) - 1
    th, tm = map(int, tt.split(':'))
    f = fd * 24 * 60 + fh * 60 + fm
    t = td * 24 * 60 + th * 60 + tm
    T.append((f, t))

T.sort(key=lambda x: (x[1], x[0]))
ans = 0
end_times = []
for left, right in T:
    idx = bisect_left(end_times, left)
    if idx > 0:
        del end_times[idx - 1]
        end_times.append(right)
        ans += 1
    elif len(end_times) < n:
        end_times.append(right)
        ans += 1
print(ans)