def sleep(H, M, h, m):
    if H > h or (H == h and M > m):
        h += 24
    return h * 60 + m - H * 60 - M


N = int(input())
total = 0
for n in range(N):
    HM, hm = input().split()
    H, M = map(int, HM.split(':'))
    h, m = map(int, hm.split(':'))
    total += sleep(H, M, h, m)
print(total)