N=int(input())
sleep=0
for _ in range(N):
    IN,OUT=input().split()
    H,M=IN.split(":")
    h,m=OUT.split(":")
    H,M,h,m=int(H),int(M),int(h),int(m)
    if h<=H and H<=23:
        sleep+=(((23-H)*60+(60-M))+h*60+m)
    elif 0<=H and H<=h:
        if m>M:
            sleep+=((h-H)*60+(m-M))
        elif m==0 and M!=0:
            sleep+=((h-H-1)*60+(60-M))
        elif m<M:
            sleep+=((h-H-1)*60+(60-(M-m)))
        elif m==M:
            sleep+=((h-H)*60)
print(sleep)