N = int(input())


def culSleepTime(slsh, slsm, sleh, slem):
    if slsh > sleh:
        return ((sleh+24)*60 + slem) - (slsh*60 + slsm)
    elif slsh == sleh:
        if slsm > slem:
            return ((sleh+24)*60 + slem) - (slsh*60 + slsm)
        else:
            return (sleh*60 + slem) - (slsh*60 + slsm)
    else:
        return (sleh*60 + slem) - (slsh*60 + slsm)
culSleepTime

total_sleeprecord = 0
for i in range(N):
    s_start, s_end = input().split()
    s_start_h, s_start_m = s_start.split(":")
    s_end_h, s_end_m = s_end.split(":")
    total_sleeprecord += culSleepTime(int(s_start_h), int(s_start_m), int(s_end_h), int(s_end_m))

print(total_sleeprecord)