# coding:utf-8
n = int(input())
total = 0
for i in range(n):
    s, g = map(str, input().split())
    sl = list(map(int,s.split(':')))
    gl = list(map(int,g.split(':')))
    if gl[0] - sl[0] < 0:
        dt1 = gl[0] + 24 - sl[0]
        dt2 = gl[1] - sl[1]
    else:
        dt1 = gl[0] - sl[0]
        dt2 = gl[1] - sl[1]
    total += (dt1 * 60) + dt2
print(total)