n = int(input())
input_list = []

for i in range(n):
    input_list.append(list(input().split()))

amount = 0
for e in input_list:
    down_h, down_m = map(int, str(e[0]).split(':'))
    up_h, up_m = map(int, str(e[1]).split(':'))

    sleep_m = up_m - down_m
    sleep_h = up_h - down_h

    if sleep_h == 0 and sleep_m < 0:
        sleep_h += 24

    if sleep_h < 0:
        sleep_h += 24

    if sleep_m < 0:
        sleep_h -= 1
        sleep_m += 60

    if sleep_m >= 60:
        sleep_h += 1
        sleep_m -= 60

    amount += (sleep_h * 60) + sleep_m

print(amount)