import re
N = int(input())
a = 0
for i in range(N):
    h1, m1, h2, m2 = map(int, re.split('[ :]', input()))
    d = (h2 * 60 + m2) - (h1 * 60 + m1)
    if d < 0:
        d += 24 * 60
    a += d
print(a)