def ji(h):
	hour, min = [int(x.strip()) for x in h.split(':')]
	min = hour*60 + min
	return min-720 if 720 < min else 720 + min

ans = 0
for _ in '1'*int(input()):
	a,b = input().split()
	ans += ji(b) - ji(a)
print(ans)