# coding:utf-8
import datetime
n = int(input())
total = datetime.timedelta(hours=0,minutes=0)
for i in range(n):
    s, g = map(str, input().split())
    sl = s.split(':')
    gl = g.split(':')
    st = datetime.timedelta(days=-1,hours=int(sl[0]),minutes=int(sl[1]))
    gt = datetime.timedelta(days=0,hours=int(gl[0]),minutes=int(gl[1]))
    total += abs(gt - st)
s_time = total - datetime.timedelta(days=1)
ans = s_time.seconds // 60
print(ans)