n,s=map(int,input().split())
a=[*range(1,n+1)]
ans=[]
while s!=0 or len(a)!=0:
    c=a.pop()
    if s-c>=0:
        s-=c
        ans.append(c)
if s!=0:exit(print(-1))
print(len(ans))
ans.sort()
print(*ans)