import java.io.*;
import java.util.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        long s = sc.nextLong();
        if (n * (n + 1L) / 2 < s) {
            System.out.println("-1");
            return;
        }
        ArrayList<Integer> ans = new ArrayList<>();
        StringBuilder sb = new StringBuilder();
        int count = 0;
        for (int i = n; i >= 1; i--) {
            if (s >= i) {
                count++;
                s -= i;
                ans.add(i);
            }
        }
        System.out.println(count);
        for (int i = ans.size() - 1; i >= 0; i--) {
            if (i < ans.size() - 1) {
                sb.append(" ");
            }
            sb.append(ans.get(i));
        }
        System.out.println(sb);
    }
}
class Utilities {
    static String arrayToLineString(Object[] arr) {
        return Arrays.stream(arr).map(x -> x.toString()).collect(Collectors.joining("\n"));
    }
    
    static String arrayToLineString(int[] arr) {
        return String.join("\n", Arrays.stream(arr).mapToObj(String::valueOf).toArray(String[]::new));
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public int[] nextIntArray() throws Exception {
        return Stream.of(br.readLine().split(" ")).mapToInt(Integer::parseInt).toArray();
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}