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()
    a,b=x.split(":")
    c,d=y.split(":")
    a,b,c,d=map(int,[a,b,c,d])
    ans+=timer(a,b,c,d)
print(ans)