## https://yukicoder.me/problems/no/580

def main():
    N, M = map(int, input().split())
    lists = []
    for _ in range(M):
        d, hhmmd, o, hhommo = input().split()

        d = int(d)
        hhd, mmd = map(int, hhmmd.split(":"))
        o = int(o)
        hho, mmo = map(int, hhommo.split(":"))

        s = (d -2 ) * (60 * 24) + hhd * 60 + mmd
        g = (o -2 ) * (60 * 24) + hho * 60 + mmo
        lists.append((s, g))

    lists.sort(key=lambda x : x[1] * 1000000 + x[0])

    room_ends = [-2] * N
    answer = 0
    for s, g in lists:
        target_s = -float("inf")
        target_n = -1
        for n in range(N):
            if room_ends[n] < s:
                if room_ends[n] > target_s:
                    target_s = room_ends[n]
                    target_n = n

        if target_n != -1:
            room_ends[target_n] = g
            answer += 1
            
    print(answer)
        
                

    











if __name__ == '__main__':
    main()