N,S=map(int,input().split())
ans = []
s = N*(N+1)//2
for i in range(N,0,-1):
    if s-S>=i:
        s-=i
    else:
        ans.append(i)
if len(ans)>0:
    print(len(ans))
    print(*ans[::-1])
else:
    print(-1)