N = int(input())
t = 0
for _ in range(N):
    H, M, h, m = [int(i) for i in input().replace(":"," ").split(" ")]
    if H > h or (H == h and M > m):
        t += (23 - H) * 60 + (60 - M) + ((h * 60) + m)
    else:
        t +=  ((h * 60) + m) - ((H * 60) + M)
print(t)