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

def calc(H, M, h, m):
    S = 60 * H + M
    B = 24 * 60
    if H <= h:
        W = 60 * h + m
    else:
        W = 60 * h + m + B
    if W < S:
        W += 24 * 60
    return W - S


N = input()
tot = 0
for i in range(0, N):
    S, W = raw_input().split()
    H, M = map(int, S.split(":"))
    h, m = map(int, W.split(":"))
    tot += calc(H, M, h, m)
print tot