# #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
res = 1
initX = vX[K-1]
initA = vA[K-1]

# for plus
prevX, prevA = initX, initA
for i in range(K, N):
    dist = abs(vX[i] - prevX)
    dprint(dist, i, res)
    if dist > prevA:
        break
    else:
        res += 1
        prevX, prevA = vX[i], vA[i]

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

print(res)