#coding=UTF-8

def timetomin(mojir):
    hyo=mojir.split(':')
    H=int(hyo[0])
    M=int(hyo[1])
    return H*60+M

N=int(input())

ans=0
for idx in range(0,N,1):
    mojir=input()
    hyo=mojir.split(' ')
    roughitme=timetomin(hyo[1])-timetomin(hyo[0])
    #1回の睡眠時間は0分以上24時間未満
    if roughitme < 0:
        roughitme=roughitme+24*60
    ans=ans+roughitme

print(ans)