from collections import deque

N, K = map(int, input().split())
K -= 1
X = list(map(int, input().split()))
A = list(map(int, input().split()))

left = X[K] - A[K]
right = X[K] + A[K]
q = deque([(K-1, -1), (K+1, 1)])
used = {K}  # 鳴いたカエル
while q:
    p, d = q.popleft()
    if not (0 <= p < N): continue

    if d == -1:
        if left <= X[p]:
            used.add(p)
            left = min(left, X[p] - A[p])
            right = max(right, X[p] + A[p])
            q.append((p-1, -1))

    else:
        if X[p] <= right:
            used.add(p)
            left = min(left, X[p] - A[p])
            right = max(right, X[p] + A[p])
            q.append((p+1, 1))

print(len(used))