#include <iostream>
#include <cmath>
#include <algorithm>
#include <math.h>
#include <vector>
#include <fstream>

using namespace std;
void BackTracking(int nCoin);

int N, M;


vector<int> ans;
vector<int> coinsIn;

void doSearch(int nCoin, long long sum, vector<int> &usedCoins) {
    //cout << "nCoin " << nCoin << " summ " << sum << " N " << N << " M " << M << endl;
    if (nCoin >= M) return;
    if (sum > N) return;



    if (sum == N) {
        if ( ans.empty() || usedCoins.size() < ans.size() ) {
            ans = usedCoins;
            /*for (int i = 0; i < usedCoins.size(); i++) {
                cout << usedCoins[i] << " ";
            }
            cout << endl;*/
        }
        return;
    }

    for (int i = 0; i <= 2; ++i) {
        if (i != 0) {
            usedCoins.push_back(coinsIn[nCoin]);
            if (i == 2) usedCoins.push_back(coinsIn[nCoin]);
        }

        /*cout << "====================" << endl;

        for (int i = 0; i < usedCoins.size(); i++) {
                cout << usedCoins[i] << " ";
            }
            cout << endl;*/

        doSearch(nCoin+1, sum + i * coinsIn[nCoin], usedCoins);


        if (i != 0) {
            usedCoins.pop_back();
            if (i == 2) usedCoins.pop_back();
        }


        /*for (int i = 0; i < usedCoins.size(); i++) {
                cout << usedCoins[i] << " ";
            }
            cout << endl;*/

        //cin.get();
    }

}

int main()
{
    long long sum;
    cin >> N >> M;


    for (int i = 0; i < M; ++i) {
        int t;
        cin >> t;
        coinsIn.push_back(t);
        sum += t*2;
    }

    if (sum < N) {
        cout << "-1";
    } else {
        vector<int> usedCoins;
        doSearch(0, 0, usedCoins);


        cout << ans.size()<< endl;
        for (int i = 0; i < ans.size(); i++) {
            cout << ans[i] << " ";
        }
    }


    return 0;
}