#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    ll N, S;
    cin >> N >> S;
    
    ll d = N * (N + 1) / 2 - S;
    set<ll> s;
    for (ll i = N; i > 0; i--) {
        if (d >= i) {
            s.insert(i);
            d -= i;
        }
    }
    
    cout << N - s.size() << '\n';
    
    rep(i, 1, N + 1) {
        if (!s.count(i)) cout << i << ' ';
    }
    cout << '\n';
}