N = int(input())
def f(a):
	a = list(map(int,a.split(':')))
	return a[0]*60+a[1]
def g(a):
	if a[1] > a[0]: return a[1]-a[0]
	else:return a[1]-(a[0]-1440)
sum = 0
for i in range(N):
	sum = sum + g(list(map(f,input().split())))
print(sum)