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

    hours = 0
    minutes = 0
    for t1, t2 in T:
        h1, m1 = map(int, t1.split(':'))
        h2, m2 = map(int, t2.split(':'))
        hours += min(abs(h2 - h1), 24 - abs(h2 - h1))
        minutes += m2 - m1

    ans = hours * 60 + minutes
    print(ans)

main()