n, s = map(int, input().split())

if s > (1 + n) * n // 2:
    print(-1)
else:
    nouse = set()
    r = (1 + n) * n // 2 - s
    for i in range(n, 0, -1):
        if i <= r:
            nouse.add(i)
            r -= i
    ans = [i for i in range(1, n + 1) if i not in nouse]
    print(len(ans))
    print(*ans)