#coding: utf-8
##yuki_70

def hm(s):
 if len(s)==5:
  h=s[0]+s[1]
  m=s[3]+s[4]
 elif len(s)==4:
  if s[1]==':':
   h='0'+s[0]
   m=s[2]+s[3]
  elif s[2]==':':
   h=s[0]+s[1]
   m='0'+s[3]
 elif len(s)==3:
  h='0'+s[0]
  m='0'+s[2]
 return int(h)*60+int(m) #minutes

n=int(raw_input())
res=0
for i in xrange(n):
 t=raw_input().split()
 et=0
 et=hm(t[1])-hm(t[0])
 if et<0:
  et=et+60*24
 res+=et

print res