import sys; input = sys.stdin.buffer.readline
sys.setrecursionlimit(10**7)
from collections import defaultdict
con = 10 ** 9 + 7; INF = float("inf")
from collections import deque
import bisect

def getlist():
	return list(map(int, input().split()))

class Graph(object):
	def __init__(self):
		self.graph = defaultdict(list)

	def __len__(self):
		return len(self.graph)

	def add_edge(self, a, b):
		self.graph[a].append(b)

class BFS(object):
	def __init__(self, graph, s, N):
		self.g = graph.graph
		self.Q = deque(); self.Q.append(s)
		self.dist = [INF] * N; self.dist[s] = 0
		while self.Q:
			v = self.Q.popleft()
			for i in self.g[v]:
				if self.dist[i] == INF:
					self.dist[i] = self.dist[v] + 1
					self.Q.append(i)

#処理内容
def main():
	N, K = getlist()
	X = getlist()
	A = getlist()

	G = Graph()
	for i in range(K - 1):
		G.add_edge(i, i + 1)
	for i in range(K - 1, N):
		G.add_edge(i + 1, i)

	for i in range(N):
		left = bisect.bisect_left(X, X[i] - A[i])
		right = bisect.bisect_right(X, X[i] + A[i]) - 1
		G.add_edge(i, left)
		G.add_edge(i, right)

	BF = BFS(G, K - 1, N)
	ans = 0
	for i in range(N):
		if BF.dist[i] != INF:
			ans += 1

	print(ans)



if __name__ == '__main__':
	main()