# #debug
def dprint(*ar):
    # print(*ar)
    pass


N, K = map(int, input().split())
vX = list(map(int, input().split()))
vA = list(map(int, input().split()))

# init
# 0-origin
initX = vX[K-1]
initA = vA[K-1]
L, R = (initX-initA), (initX+initA)

for _ in range(N):
    # for plus
    prevX, prevA = initX, initA
    for i in range(K, N):
        dist = abs(vX[i] - prevX)
        dprint(dist, i, L, R)
        if dist > prevA:
            break
        else:
            prevX = vX[i]
            prevA = max(vA[i], prevA - dist)
            R = max(R, prevX + prevA)
            L = min(L, prevX - prevA)

    # for minus
    prevX, prevA = initX, initA
    for i in range(K-2, -1, -1):
        dist = abs(vX[i] - prevX)
        dprint(dist, i, L, R)
        if dist > prevA:
            break
        else:
            prevX = vX[i]
            prevA = max(vA[i], prevA - dist)
            R = max(R, prevX + prevA)
            L = min(L, prevX - prevA)

res = sum([L<=x<=R for x in vX])
print(res)