N = int(input())
records = [input().split() for _ in range(N)]

ans = 0
for a, b in records:
    h_st, m_st = map(int, a.split(":"))
    h_end, m_end = map(int, b.split(":"))
    if h_st > h_end:
        ans += (23 - h_st + h_end) * 60 + (60 - m_st + m_end)
    else:
        ans += (h_end - h_st) * 60 + (m_end - m_st)

print(ans)