def get_sleeping_time(start:str,end:str):
    start = time_to_minutes(start)
    end = time_to_minutes(end)
    st = end - start
    if st < 0:
        st+=24 * 60
    return st

def time_to_minutes(_time:str):
    h,m = map(int,_time.split(":"))
    return h * 60 + m

N = int(input())
sleeping_time = [get_sleeping_time(*input().split()) for x in range(N)]
print(sum(sleeping_time))