#include <bits/stdc++.h>

#include <variant>

#define rep2(i, k, n) for (i64 i = (i64)(k); i < (i64)(n); i++)
#define rep(i, n) rep2(i, 0, n)
#define all(x) begin(x), end(x)
#ifdef ENV_LOCAL
#define dump \
  if (1) cerr
#else
#define dump \
  if (0) cerr
#endif

using namespace std;
using namespace std::string_literals;

using i32 = int32_t;
using i64 = int64_t;
using f64 = double;
using f80 = long double;
using vi32 = vector<i32>;
using vi64 = vector<i64>;

// using namespace harudake;

int main() {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  i64 n, s;
  cin >> n >> s;
  vi64 ans;
  rep(ri, n) {
    i64 i = n - ri;
    if (i <= s) {
      ans.push_back(i);
      s -= i;
    }
  }
  if (s == 0) {
    reverse(all(ans));
    cout << size(ans) << endl;
    rep(i, size(ans)) {
      if (i) cout << " ";
      cout << ans[i];
    }
    cout << endl;
  } else {
    cout << -1 << endl;
  }
  return 0;
}