#yuki1915
import heapq
N, K = map(int, input().split())
q = [(0,0, [])] #sum upper
heapq.heapify(q)
while q:
    s, u, vis = heapq.heappop(q)
    for a in range(u + 1, N + 1):
        ns = s +  a
        nu = a
        nvis = vis + [a]
        if ns == K:
            print(len(nvis))
            print(" ".join(map(str, nvis)))
            exit()
        if a < N:
            heapq.heappush(q, (ns, nu, nvis))
print(-1)