#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll = long long;
using ld = long double;
using mint = modint998244353;

int main() {
  ll n, s; cin >> n >> s;
  ll sum = 0;
  vector<ll> vec;
  for (ll i = n; i >= 1; i--) {
    if (sum + i <= s) {
      sum += i;
      vec.push_back(i);
    }
  }
  if (sum == s) {
    reverse(vec.begin(), vec.end());
    cout << vec.size() << endl;
    for (int i = 0; i < vec.size(); i++) cout << vec[i] << " \n"[i == vec.size() - 1];
  } else {
    cout << -1 << endl;
  }
  return 0;
}