n=int(input())

cnt=0
for i in range(n):
    hm1,hm2=map(str,input().split())
    h1,m1=map(int,hm1.split(':'))
    h2,m2=map(int,hm2.split(':'))
    time1=h1*60+m1
    time2=h2*60+m2
    cnt+=(time2-time1)%1440

print(cnt)