n = int(input())
hour_list = []
minute_list = []
res = 0

for i in range(n):
    times = input()
    times_split = times.split(' ')
    
    for i in range(2):
        hour, minute = times_split[i].split(':')
        hour_list.append(int(hour))
        minute_list.append(int(minute))
    
    if hour_list[0] == hour_list[1] and minute_list[0] > minute_list[1]:
        res += 24 * 60 - minute_list[0]
    else:
        if hour_list[0] > hour_list[1]:
            res += 60 * ((24 - hour_list[0]) + hour_list[1])
        else:
            res += 60 * (hour_list[1] - hour_list[0])

        res += minute_list[1] - minute_list[0]
    
    hour_list.clear()
    minute_list.clear()

print(res)