#include<bits/stdc++.h>
#define ll long long
#define pb push_back
using namespace std;

ll ar[30];
ll arr[30];
vector <ll> answer;
bool q = false;
ll n, m;

bool check(){
    ll sum = 0;
    for (ll i = 0; i < m; ++i){
        sum += ar[i] * arr[i];
    }
    return sum == n;
}

void rek(ll a){
    if (a >= m){
        if (check()) {
            ll ans = 0;
            for (ll i = 0; i < m; ++i){
                ans += ar[i];
            }
            if ((!q) || (ans < answer.size())){
                q = true;
                answer.clear();
                for (ll i = 0; i < m; ++i){
                    if (ar[i] == 1) answer.pb(arr[i]);
                    else if (ar[i] == 2) {
                        answer.pb(arr[i]);
                        answer.pb(arr[i]);
                    }
                }
            }
        }
        return;
    }
    for (ll i = 0; i < 3; ++i){
        ar[a] = i;
        rek(a + 1);
    }
}

int main(){
    cin>>n>>m;
    ll sum = 0;
    for (ll i = 0; i < m; ++i){
        cin>>arr[i];
        sum += arr[i] * 2;
    }
    if (sum < n){
        cout<<-1;
        exit(0);
    }
    rek(0);
    if (q){
        cout<<answer.size()<<endl;
        for (ll i = 0; i < answer.size(); ++i){
            cout<<answer[i]<<" ";
        }
        exit(0);
    }
    cout<<0;
}