N = input()
timeSum = 0
for i in range(N):
	a = raw_input().replace(':',' ').split()
	sleep = int(a[0])*60+int(a[1])
	up = int(a[2])*60+int(a[3])
	if sleep > up:
		timeSum += ((1440 - sleep) + up)
	else:
		timeSum += (up - sleep)
print timeSum