N, S = map(int, input().rstrip().split())

if not 1 <= S <= N*(N+1)//2:
    print(-1)
else:
    remain = S
    ans = []
    for i in range(N, 0, -1):
        if i <= remain:
            remain -= i
            ans.append(i)
        
    print(len(ans))
    print(*ans[::-1])