#!/usr/bin/env python3
#fileencoding: utf-8

N = int(input())
total = 0
for i in range(N):
    slp, wkup = input().strip().split(" ")
    slp_h, slp_m = [int(j) for j in slp.split(":")]
    wkup_h, wkup_m = [int(j) for j in wkup.split(":")]
    if slp_h > wkup_h or ((slp_h == wkup_h) and (slp_m > wkup_m)):
        wkup_h += 24
    slp_time = slp_h * 60 + slp_m
    wkup_time = wkup_h * 60 + wkup_m
    total += (wkup_time - slp_time)
print(total)