#!/usr/bin/python
from datetime import datetime, timedelta
f = lambda s: datetime.strptime(s, '%H:%M')

n = int(raw_input())
res = 0
for _ in xrange(n):
    fra, to = map(f, raw_input().split())
    if fra > to:
        to += timedelta(days=1)
    res += (to - fra).total_seconds()

print int(res / 60)