N = input()
ans = 0
for i in range(N):
    S, T = raw_input().strip().split(" ")
    h, m = map(int, S.split(":"))
    t0 = h * 60 + m
    h, m = map(int, T.split(":"))
    t1 = h * 60 + m
    ans += t1 - t0
    if t1 < t0:
        ans += 1440
print(ans)