#include <bits/stdc++.h>
using namespace std;

using ll = long long;
#define rep(i, n) for(ll i = 0; i < n; i++)

int main() {
	ll N, s;
	cin >> N >> s;
	for(ll i = 1; i <= N; i++) {
		ll m = i * (i + 1) / 2;
		if(m >= s) {
			int k = i;
			int d = m - s;
			if(d) k--;
			cout << k << endl;
			for(int j = 1; j <= i; j++) {
				if(j == d) continue;
				cout << j << " ";
			}
			cout << endl;
			return 0;
		}
	}
	cout << -1 << endl;
}