import java.io.*;
import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        int n = in.nextInt(), t = in.nextInt();
        int[] arr = new int[n + 1], arr_v = new int[t];

        for (int i = 0; i < t; i++) {
            arr_v[i] = in.nextInt();
        }

        for (int i = 1; i < n + 1; i++) {
            int min = 20000000;
            for (int j = t - 1; j >= 0; j--) {
                if (i - arr_v[j] >= 0) {
                    min = Math.min(min, arr[i - arr_v[j]]);
                }
            }
            arr[i] = 1 + min;
        }

        if (arr[n] > 20000000) System.out.println(-1);
        else System.out.println(arr[n]);


        int e = n;
        for (int i = arr[n]; i > 0; i--) {
            for (int j = t - 1; j >= 0; j--) {
                if (e - arr_v[j] >= 0 && arr[e - arr_v[j]] == arr[e] - 1) {
                    System.out.print(arr_v[j] + " ");
                    e -= arr_v[j];
                }
            }
        }

        in.close();
    }
}