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

l = r = K - 1
ld, rd = X[K - 1] - A[K - 1], X[K - 1] + A[K - 1]


updated = True
while updated:
    updated = False

    while (l - 1 >= 0) and (ld <= X[l - 1]):
        updated = True
        l -= 1
        ld = min(ld, X[l] - A[l])
        rd = max(rd, X[l] + A[l])

    while (r + 1 < N) and (rd >= X[r + 1]):
        updated = True
        r += 1
        ld = min(ld, X[r] - A[r])
        rd = max(rd, X[r] + A[r])

print(r - l + 1)