def main():
    N = int(input())
    T = tuple(tuple(input().split()) for _ in [0] * N)

    minutes = 0
    for t1, t2 in T:
        h1, m1 = map(int, t1.split(':'))
        h2, m2 = map(int, t2.split(':'))
        m = (h2 * 60 + m2) - (h1 * 60 + m1)
        if m <= 0:
            minutes += m + 24 * 60
        else:
            minutes += m

    print(minutes)

main()