#coding: UTF-8

import sys
from math import pi
from collections import deque
from functools import reduce

### defs ###

### main ###
N = int(sys.stdin.readline())
HMhm = map(lambda s:s.split(), map(lambda s:s.strip('\r\n'),sys.stdin.readlines()))
HMhm = map(lambda lst: list(map(lambda s:s.split(':'),lst)) , HMhm)
HMhm = map(lambda lst: list(map(lambda tm:int(tm[0])*60+int(tm[1]),lst)) , HMhm)
HMhm = map(lambda lst: [lst[0],lst[1]+60*24] if lst[1]<lst[0] else [lst[0],lst[1]] ,HMhm)
print(sum(map(lambda lst: lst[1]-lst[0],HMhm)))