n = int(input())


def f(hm):
    h, m = map(int, hm.split(":"))
    return 60 * h + m


ans = 0
for _ in range(n):
    hm1, hm2 = input().split()
    ans += (f(hm2) - f(hm1)) % (24 *  60)

print(ans)