#include <iostream>
#include <set>
using namespace std;

int main(){
    long long n,s;cin>>n>>s;
    s = n*(n+1)/2-s;
    set<long long> a;
    for(int i = n; i >= 1; i--){
        if(s >= i){
            s -= i;
            a.insert(i);
        }
    }
    bool ex = false;
    cout << n-a.size() << endl;
    for(int i = 1; n >= i; i++){
        if(a.count(i))continue;
        if(ex)cout << " ";
        else ex = true;
        cout << i;
        
    }
    cout << endl;
}