n = int(input())
ans=0
for i in range(n):
    s1,s2 = input().split()
    h1,m1 = map(int,s1.split(":"))
    h2,m2 = map(int,s2.split(":"))
    r = (h2 * 60 + m2) - (h1 * 60 + m1)
    if r <0:
        r += 24*60
    ans+=r

print(ans)