n = int(raw_input())
ans = 0

for i in range(0, n):
	s = raw_input().split()
	gobed = map(int, s[0].split(':'))
	getup = map(int, s[1].split(':'))
	if getup[0] < gobed[0]:
		getup[0] += 24
	h = getup[0] - gobed[0]
	if getup[1] < gobed[1]:
		h -= 1
		getup[1] += 60
	m = getup[1] - gobed[1]
	ans += h * 60 + m

print ans