n = int(input())

time_lst = [ list(map(str, input().split(' '))) for i in range(n) ]
time = 0
for time_pair in time_lst:
    time_sleep = time_pair[0]
    time_awake = time_pair[1]
    time_sleep_hour, time_sleep_minute = map(int, time_sleep.split(':'))
    time_awake_hour, time_awake_minute = map(int, time_awake.split(':'))

    hour_to_sleep = time_awake_hour - time_sleep_hour
    minute_to_sleep = time_awake_minute - time_sleep_minute
    if minute_to_sleep < 0:
        minute_to_sleep += 60
        hour_to_sleep -= 1
    
    if hour_to_sleep < 0:
        hour_to_sleep += 24

    time += minute_to_sleep
    time += hour_to_sleep*60


print(time)