N = int(input())

def sleeping_sec(time_to_sleep,time_to_wake_up):
    import datetime

    neru_hour, neru_min = map(int, time_to_sleep.split(":"))
    okita_hour, okita_min = map(int, time_to_wake_up.split(":"))

    day1 = 1

    if neru_hour > okita_hour:
        day2 = 2
    elif neru_hour == okita_hour:
        if neru_min > okita_min:
            day2 = 2
        else:
            day2 = 1
    else :
        day2 = 1


    first_time = datetime.datetime(2018, 3, day1, neru_hour, neru_min)
    last_time = datetime.datetime(2018, 3, day2, okita_hour, okita_min)
    delta = last_time - first_time
    return(delta.total_seconds())


sleep_time_l = []

for _ in range(N):
    l = input().split()
    sleep_time_l.append(sleeping_sec(l[0], l[1]))

print(int(sum(sleep_time_l)/60))