N=int(input())
sleep=0
for _ in range(N):
    IN,OUT=input().split()
    H,M=map(int,IN.split(":"))
    h,m=map(int,OUT.split(":"))
    time=(h*60+m)-(H*60+M)
    if time<0:
        time+=24*60
    sleep+=time
print(sleep)