N = int(input())
HMhm = [input().split() for _ in range(N)]
ans = 0
for HM, hm in HMhm:
    H, M = map(int, HM.split(":"))
    h, m = map(int, hm.split(":"))
    MM = H*60+M
    mm = h*60+m
    if mm<MM:
        mm+=24*60
    ans+=mm-MM
print(ans)