def T(s):
  h,m=map(int,s.split(':'))
  return h*60+m
  
h=m=0
H=lambda s:s.split(':')[0]
M=lambda s:s.split(':')[1]
for i in '.'*int(input()):
  s,e=input().split()
  a,b=T(s),T(e)
  b+=(a>b)*1440
  m+=b-a