# -*- coding: utf-8 -*-
# n = int(input())
import datetime

today = datetime.datetime.now()
tomorrow = today + datetime.timedelta(days=1)

n = int(input())

seconds = 0
for i in range(n):
    s, e = [j for j in input().split()]
    sh, sm = [int(j) for j in s.split(":")]
    eh, em = [int(j) for j in e.split(":")]

    if datetime.time(sh, sm) <= datetime.time(eh, em):
        start = datetime.datetime(today.year, today.month, today.day, sh, sm, 0)
        end = datetime.datetime(today.year, today.month, today.day, eh, em, 0)
    else:
        start = datetime.datetime(today.year, today.month, today.day, sh, sm, 0)
        end = datetime.datetime(tomorrow.year, tomorrow.month, tomorrow.day, eh, em, 0)

    delta = end - start
    seconds += delta.total_seconds()

print( int(seconds / 60) )