# -*- coding:utf-8 -*-
def hm_to_m(hm):
    return hm[0] * 60 + hm[1]


if __name__ == '__main__':
    n = int(input())
    cnt = 0
    for i in range(n):
        hm1, hm2 = (tuple(map(int, hm.split(":"))) for hm in input().split())
        cnt += (hm_to_m(hm2) - hm_to_m(hm1)) % (60 * 24)
    print(cnt)