"""ヤブイヌよりサメさんポーチ派"""

n = int(input())
f = lambda x: x[0] * 60 + x[1]
sum_min = 0

for i in range(n):
    sleep, wake = input().split()
    s_time = f(list(map(int, sleep.split(':'))))
    w_time = f(list(map(int, wake.split(':'))))
    sum_min += w_time - s_time if w_time >= s_time else w_time - s_time + 60 * 24

print(sum_min)