def timecalc(h, m):
	return 60*h+m
N = int(raw_input())
sum = 0
for i in range(0, N):
	inpt = raw_input().split()
	sleep = map(int, inpt[0].split(':'))
	awake = map(int, inpt[1].split(':'))
	sm = timecalc(sleep[0], sleep[1])
	wm = timecalc(awake[0], awake[1])
	if wm < sm: sum += (1440-sm) + wm
	else: sum += wm-sm
print sum