#include <bits/stdc++.h>
#define int long long

using namespace std;

vector <int> num, now;
vector <vector<int> > ans;
int n;

vector <int> rev(vector <int> num) {
    vector <int> res;
    for (int i = num.size() - 1; i > -1; i--) {
        res.push_back(num[i]);
    }
    return res;
}

void a(int pos, int sum) {
    if (sum == n) {
        //cout << "aaaaaaaaaaaaaaaaaa\n";
        ans.push_back(now);
    }
    else if (sum > n) {
        //cout << "bbbbbbbbbbbbbbbbb\n";
        return;
    }
    else {
        for (int i = pos + 1; i < num.size(); i++) {
            //cout << "jfdsifhusd\n";
            now.push_back(num[i]);
            a(i, sum + num[i]);
            now.pop_back();
        }
    }
}

int32_t main() {
    int m;
    cin >> n >> m;
    int k = 0;
    for (int i = 0; i < m; i++) {
        int a;
        cin >> a;
        num.push_back(a);
        num.push_back(a);
        k += a * 2;
    }
    sort(num.begin(), num.end());
    if (k < n) {
        cout << -1 << "\n";
        return 0;
    }

    num = rev(num);
    //for (int i = 0; i < num.size(); i++) cout << num[i] << " ";
    //cout << "\n";
    a(-1, 0);
    if (ans.size() == 0) {
        if (k >= n) {
            cout << 0 << "\n";
            return 0;
        }
        cout << -1 << "\n";
        return 0;
    }
    cout << ans[0].size() << " ";
    for (int i = 0; i < ans[0].size(); i++) {
        cout << ans[0][i] << " ";
    }
    return 0;
}