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

left, right = K, K
left_range, right_range = X[K] - A[K], X[K] + A[K]
while True:
    update = False
    while left != 0 and X[left-1] >= left_range:
        left -= 1
        left_range = min(left_range, X[left] - A[left])
        right_range = max(right_range, X[left]+A[left])
        update = True
    while right != N-1 and X[right+1] <= right_range:
        right += 1
        left_range = min(left_range, X[right] - A[right])
        right_range = max(right_range, X[right] + A[right])
        update = True
    if not update:
        break
print(right - left + 1)