n, m = map(int, input().split())

l = []
x = 0
y = 0
for _ in range(m):
    a, b, c, d = input().split()
    x += int(a) * 60 * 24
    e, f = map(int, b.split(':'))
    x += e*60 + f
    y += int(c) * 60 * 24
    g, h = map(int, d.split(':'))
    y += g*60 + h
    l.append([y, x])
    x = 0
    y = 0
l = sorted(l)
# print(l)

r = [0] * n
z = 0
for i in range(m):
    for j in range(n):
        if r[j] < l[i][1]:
            r[j] = l[i][0]
            z += 1
            r = sorted(r)[::-1]
            l[i][1] = 0
            # print(r)

print(z)