N = int(input())
num = 0
for i in range(N):
    a, b = input().split()
    H, M = map(int, a.split(":"))
    h, m = map(int, b.split(":"))

    m1 = m - M
    if m1 < 0:
        h -= 1
        m1 += 60

    h1 = h - H
    if h1 < 0:
        h1 += 24

    num += h1 * 60 + m1

print(num)