import sys, math
sys.setrecursionlimit(1000000)
INF = 1 << 100
#mod = 1000000007
mod = 998244353
input = lambda: sys.stdin.readline().rstrip()
li = lambda: list(map(int, input().split()))

N, S = li()
A = [i for i in range(1, N+1)]


ans = []
for a in A[::-1]:
    if S >= a:
        ans.append(a)
        S -= a

ans.sort()
if S > 0:
    print(-1)
    exit()
print(len(ans))
print(*ans)