#include <iostream>
#include <vector>
#include <cmath>
#include <map>
#include <set>
#include <iomanip>
#include <queue>
#include <algorithm>
#include <numeric>
#include <deque>
#include <complex>
#include <cassert>

using namespace std;
using ll = long long;

int main(){

    ll N, S;
    cin >> N >> S;
    vector<ll> v;

    for (ll i=N; i>=1; i--){
        if (S >= i){
            S -= i;
            v.push_back(i);
        }
    }

    if (S > 0) cout << -1 << endl;
    else{
        reverse(v.begin(), v.end());
        cout << v.size() << endl;
        for (auto x : v) cout << x << " ";
        cout << endl;
    }

    return 0;
}