def getSleepTime(s):
    start, end = s.split(" ")
    start = list(map(int, start.split(":")))
    end = list(map(int, end.split(":")))
    if start[0]*60 + start[1] > end[0]*60 + end[1]: #分でも比較
        end[0] += 24
    s_min = start[0]*60 + start[1]
    e_min = end[0]*60 + end[1]
    return e_min - s_min

N = int(input())
print(sum([getSleepTime(input()) for i in range(N)]))