import sys
from datetime import datetime
input=lambda:sys.stdin.readline().rstrip()
def trans(S):
	return datetime.strptime(S,"%H:%M")
N,ans=int(input()),0
for i in range(N):
	temp=input().split()
	ans+=(trans(temp[1])-trans(temp[0])).total_seconds()//60%(24*60)
print(int(ans))