n = int(input())
ans = 0
for i in range(n):
    a,b = input().split()
    H,M = map(int,a.split(":"))
    h,m = map(int,b.split(":"))

    a = H*60+M
    b = h*60+m
    if a <= b:
        ans += b-a
    else:
        ans += b+60*24-a
print(ans)