n, k = map(int, input().split())
x = list(map(int, input().split()))
a = list(map(int, input().split()))
left = list(range(k-1))
right = list(range(n-1, k-1, -1))
lm, rm = x[k-1]-a[k-1], x[k-1]+a[k-1]

while True:
	left_ok, right_ok = False, False
	if left != [] and x[left[-1]] >= lm:
		left_ok = True
		lm = min(lm, x[left[-1]]-a[left[-1]])
		rm = max(rm, x[left[-1]]+a[left[-1]])
		left.pop()
	if right != [] and x[right[-1]] <= rm:
		right_ok = True
		lm = min(lm, x[right[-1]]-a[right[-1]])
		rm = max(rm, x[right[-1]]+a[right[-1]])
		right.pop()
	if not left_ok and not right_ok:
		break

print(n-len(left)-len(right))