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])
update = True
while update:
    update = False

    hd = q[0]
    if hd > 0 and left <= X[hd-1]:
        update = True
        left = min(left, X[hd-1] - A[hd-1])
        right = max(right, X[hd-1] + A[hd-1])
        q.appendleft(hd-1)

    tl = q[-1]
    if tl+1 < N and X[tl+1] <= right:
        update = True
        left = min(left, X[tl+1] - A[tl+1])
        right = max(right, X[tl+1] + A[tl+1])
        q.append(tl+1)

print(len(q))