//https://ncode.syosetu.com/n4830bu/247/
#include <bits/stdc++.h>
using namespace std;

int main() {
    int C, N;
    cin >> C >> N;
    vector<int> A(N);
    for (auto&& a : A) {
        cin >> a;
    }
    const int INF = 1e7;
    vector dp(C + 1, INF);
    dp[0] = 0;
    for (auto&& a : A) {
        for (int i = 0; i < C + 1; i++) {
            int nxt = i + a;
            if (nxt > C)
                break;
            dp[nxt] = min(dp[nxt], dp[i] + 1);
        }
    }
    cout << (dp[C] == INF ? -1 : dp[C]) << endl;
}