#include <bits/stdc++.h>

using namespace std;

namespace {

    typedef double real;
    typedef long long ll;

    template<class T> ostream& operator<<(ostream& os, const vector<T>& vs) {
        if (vs.empty()) return os << "[]";
        os << "[" << vs[0];
        for (int i = 1; i < vs.size(); i++) os << " " << vs[i];
        return os << "]";
    }
    template<class T> istream& operator>>(istream& is, vector<T>& vs) {
        for (auto it = vs.begin(); it != vs.end(); it++) is >> *it;
        return is;
    }

    int C;
    int N;
    vector<int> A;
    void input() {
        cin >> C;
        cin >> N;
        A.clear(); A.resize(N);
        cin >> A;
    }

    const int INF = 1<<28;

    void solve() {
        auto dp = vector<int>(C + 1, INF);
        dp[0] = 0;
        for (int i = 0; i < N; i++) {
            for (int c = 0; c <= C; c++) {
                if (c - A[i] >= 0) {
                    dp[c] = min(dp[c], dp[c - A[i]] + 1);
                }
            }
        }
        if (dp[C] == INF) {
            cout << -1 << endl;
        } else {
            cout << dp[C] << endl;
        }
    }
}

int main() {
    input(); solve();
    return 0;
}