ans = 0
for i in range(int(input())):
    a = input().split()
    s = list(map(int, a[0].split(':')))
    e = list(map(int, a[1].split(':')))
    ss = s[0] * 60 + s[1]
    ee = e[0] * 60 + e[1]
    if(ss > ee):
        ee += 24 * 60
    ans += ee - ss
print(ans)