import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
ans=0
for _ in range(n):
  s,g=map(str,input().split())
  sh,sm=s.split(":")
  gh,gm=g.split(":")
  sh=int(sh)
  sm=int(sm)
  gh=int(gh)
  gm=int(gm)
  ans+=60*(gh-sh)+(gm-sm)
  if 60*(gh-sh)+(gm-sm)<0:
    ans+=60*24
print(ans)