N = int(input())

ans = 0
for _ in range(N):
    HM, hm = input().split()
    H, M = map(int, HM.split(":"))
    h, m = map(int, hm.split(":"))


    d = (60 * h + m) - (60 * H + M)
    d %= 24 * 60

    ans += d

print(ans)