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

t = 0
c = 0
l = []
for i in range(n):
    x = n-i
    if (t+x)<=s:
        l.insert(0, x)
        t += x
        c += 1
    if t == s:
        print(c)
        print(*l)
        break
else:
    print(-1)