#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void CheckSumm(int &ans, vector<int> &val, int needed_summ, int cur_summ, int count, int i) {
    if (i == val.size()){
        return;
    }
    CheckSumm(ans, val, needed_summ, cur_summ, count, i + 1);
    if (cur_summ + val[i] < needed_summ) {
        CheckSumm(ans, val, needed_summ, cur_summ + val[i], count + 1, i + 1);
    } else if (cur_summ + val[i] == needed_summ) {
        ans = min(ans, count + 1);
        return;
    } else {
        return;
    }
    if (cur_summ + 2 * val[i] < needed_summ) {
        CheckSumm(ans, val, needed_summ, cur_summ + 2 * val[i], count + 2, i + 1);
    } else if (cur_summ + 2 * val[i] == needed_summ) {
        ans = min(ans, count + 2);
        return;
    } else {
        return;
    }
}

int main() {
    int n, m;
    cin >> n >> m;
    vector<int> val;
    std::sort(val.begin(), val.end());
    std::reverse(val.begin(), val.end());
    int total_summ = 0;
    for (int i = 0; i < m; ++i) {
        int x;
        cin >> x;
        total_summ += x;
        val.emplace_back(x);
    }
    if (total_summ * 2 < n) {
        cout << -1;
        return 0;
    }
    int ans = 100;
    CheckSumm(ans, val, n, 0, 0, 0);
    if (ans == 100) {
        cout << 0;
    } else {
        cout << ans;
    }

    return 0;
}