import datetime

total = 0
n = int(input())
for i in range(n):
  t = [[int(y) for y in x.split(':')] for x in input().split(' ')]
  t1 = datetime.timedelta(hours=t[0][0], minutes=t[0][1])
  t2 = datetime.timedelta(hours=t[1][0], minutes=t[1][1])
  td = t2 - t1
  if td.seconds < 0:
    td += datetime.timedelta(hours=24)
  total += td.seconds // 60

print(total)