import datetime
def GETTIME(H0, M0, H1, M1):
    DATE0 = datetime.datetime(2023, 6, 5, H0, M0, 0)
    DATE1 = datetime.datetime(2023, 6, 5, H1, M1, 0)
    if DATE0 > DATE1:
        DATE1 = datetime.datetime(2023, 6, 6, H1, M1, 0)
    DELTA = DATE1 - DATE0
    return int(DELTA.total_seconds() / 60)
N = int(input())
ANSWER = 0
for _ in range(N):
  INPUT = input().split()
  HOURX, MINUTEX = int(INPUT[0].split(':')[0]), int(INPUT[0].split(':')[1])
  HOURY, MINUTEY = int(INPUT[1].split(':')[0]), int(INPUT[1].split(':')[1])
  ANSWER += GETTIME(HOURX, MINUTEX, HOURY, MINUTEY)
print(ANSWER)