# -*- coding: utf-8 -*-

N = int(input())
total = 0
for i in range(N):
    temp = list(input().split())
    H,M = map(int, temp[0].split(':'))
    h,m = map(int, temp[1].split(':'))
    h_diff = 0
    m_diff = 0
    if H>h:
        h += 24
        h_diff = h - H
    else:
        h_diff = h - H
    if M>m:
        m += 60
        m_diff = m - M
        h_diff -= 1
    else:
        m_diff = m - M
    if h_diff < 0:
        h_diff += 24
    total += h_diff*60 + m_diff
print(total)