n=int(input())
ans=0
def solve(a,b):
    H,M=map(int,a.split(":"))
    h,m=map(int,b.split(":"))
    if H>h:
        h+=24
    return 60*(h-H)+m-M
for i in range(n):
    hm=list(map(str,input().split()))
    ans+=solve(hm[0],hm[1])
print(ans)