def timer(a,b,c,d):
    tmp1=a*60+b
    tmp2=c*60+d
    return (tmp2-tmp1)%1440
ans=0
n=int(input())
for _ in range(n):
    x,y=input().split()
    t=x.split(":")
    u=y.split(":")
    kk=map(int,[*t,*u])
    ans+=timer(*kk)
print(ans)