import itertools as iter
import collections as coll
import heapq as hq
import bisect as bis
from decimal import Decimal as dec
from functools import cmp_to_key
import math
import sys
#import pypyjit
#pypyjit.set_param('max_unroll_recursion=-1')
sys.setrecursionlimit(10 ** 6)
inp = sys.stdin.readline
input = lambda : inp().rstrip()
getN = lambda : int(inp())
getNs = lambda : map(int, inp().split())
getList = lambda :list(map(int, inp().split()))
getStrs = lambda n : [input() for _ in [0] * n]
def yexit(): print("Yes"); exit(0)
def nexit(): print("No"); exit(0)
pi = 3.141592653589793
mod = 1000000007
MOD = 998244353
INF = 4611686018427387903
dx = [1, 0, -1, 0];	dy = [0, 1, 0, -1]


"""
Main Code
"""

n, s = getNs()
d = s // (n + 1)
r = s % (n + 1)

if(n == s and s == 1):
	print(1)
	print(1)
	exit(0)

ans = []
if(d == n // 2):
	for i in range(1, n + 1):
		if(i == n * (n + 1) // 2 - s):
			continue
		ans.append(i)
	print(len(ans))
	print(*ans)
	exit(0)

t = r
i = 0
if(r > 0):
	ans.append(r)
while(t < s):
	#print(t)
	i += 1
	if(r in [i, n + 1 - i]):
		continue
	ans.append(i)
	ans.append(n + 1 - i)
	t += n + 1
ans.sort()

if(t != s):
	print(-1)
	exit(0)

print(len(ans))
print(*ans)