N=int(input())
ans=0
for i in range(N):
  a,b=input().split()
  H,M=map(int,a.split(":"))
  h,m=map(int,b.split(":"))
  x=H*60+M
  y=h*60+m
  if x>y:
    y+=24*60
  ans+=y-x
print(ans)