def ji(h):
	hour, min = [int(x.strip()) for x in h.split(':')]
	min = hour*60 + min
	return min-720 if min>720 else 0 if min==0 else min+720

ans=0
for _ in '1'*int(input()):
	a,b = input().split()
	ans += (ji(b)-ji(a)+1440)%1440
print(ans)