# coding:utf-8
import datetime
n = int(input())
total = datetime.timedelta(hours=0,minutes=0)
for i in range(n):
    s, g = map(str, input().split())
    sl = s.split(':')
    gl = g.split(':')
    if int(sl[0]) >= 12 and int(sl[0]) < 24 :
        st = datetime.timedelta(days=-1,hours=int(sl[0]),minutes=int(sl[1]))
        gt = datetime.timedelta(days=0,hours=int(gl[0]),minutes=int(gl[1]))
        total += gt - st
    else:
        st = datetime.timedelta(days=0,hours=int(sl[0]),minutes=int(sl[1]))
        gt = datetime.timedelta(days=0,hours=int(gl[0]),minutes=int(gl[1]))
        total += gt - st

ans = total.days * 24 * 60 + total.seconds // 60
print(ans)