N = int(input())
t = 0
for i in range(N):
	s = input().split()
	b,e = (x.split(':') for x in s)
	h = (int(e[0])-int(b[0]))%24
	m = int(e[1])-int(b[1])
	t += (h*60 + m)%1440
print(t)