N = input()
Ti = list(map(lambda x: int(x)*10 - 1, input().split()))
s = list(map(lambda x: int(x)*10, input().split()))

cnt = 0
time = 0
for q, t in zip(s, Ti):
	if q > time:
		cnt += 1
		time = q + t - 1
	else:
		time = q
	
print(cnt)