N = int(input())


def f(s: str) -> int:
    h, m = map(int, s.split(':'))
    return h * 60 + m


ans = 0
for _ in range(N):
    s, t = input().split()
    a = f(s)
    b = f(t)
    if a < b:
        ans += b - a
    else:
        ans += (24 * 60 - a) + b

print(ans)