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

lt = X[K - 1] - A[K - 1]
rt = X[K - 1] + A[K - 1]

lidx = K - 1
ridx = K - 1

while True:
    update = False
    if lidx > 0 and X[lidx - 1] >= lt:
        lidx -= 1
        lt = min(lt, X[lidx] - A[lidx])
        rt = max(rt, X[lidx] + A[lidx])
        update = True
    if ridx < N - 1 and X[ridx + 1] <= rt:
        ridx += 1
        lt = min(lt, X[ridx] - A[ridx])
        rt = max(rt, X[ridx] + A[ridx])
        update = True
    if not update:
        break

print(ridx - lidx + 1)