#yuki1915
N, K = map(int, input().split())
if K <= N:
    print(K)
    exit()
if K > N*(N+1)//2:
    print(-1)
    exit()

ans = []
temp = K
for i in range(N, 0, -1):
    temp -= i
    ans.append(i)
    if temp < i - 1:
        ans.append(temp)
        ans.reverse()
        print(len(ans))
        print(*ans)
        exit()

ans.reverse()
print(len(ans))
print(*ans)
exit()