# coding: utf-8
n = int(input())

count = 0
for i in range(n):
    l = [list(map(int,i.split(":"))) for i in input().split(" ")]
    h,m = l[0]
    s = h*60 + m
    h_,m_  = l[1]
    s_ = h_*60 + m_
    if s_ < s:
        count += (24*60 - (s - s_))
    else:
        count+= (s_ - s)
print(count)