N = int(input())
t = 0
for _ in range(N):
    HM, hm = input().split()
    H, M = map(int, HM.split(':'))
    h, m = map(int, hm.split(':'))

    s = H * 60 + M
    w = h * 60 + m

    if w < s:
        w += 24 * 60
    t += w - s
print(t)