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)

ans = []

if(d < n // 2):
	if(r > 0):
		ans.append(r)
	for i in range(1, d + (r > 0)):
		if(r in [i, n + 1 - i]):
			continue
		ans.append(i)
		ans.append(n + 1 - i)
	ans.sort()
elif(n & 1):
	if(s == n * (n + 1) // 2):
		ans = [i for i in range(1, n + 1)]
	elif(s == d * (n + 1)):
		ans = [i * (i != r) for i in range(1, n + 1)]
	else:
		print(-1)
		exit(0)
else:
	ans = [i for i in range(1, n + 1)]

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