#include <iostream>
#include <algorithm>
using namespace std;

const int INF = 1 << 29;

int main() {
    int C, N;
    int a[100];

    cin >> C >> N;
    for (int j = 0; j < N; ++j) {
        cin >> a[j];
    }

    int m[100001];
    fill(m, m + 100001, INF);
    m[0] = 0;

    for (int j = 0; j < N; ++j) {
        for (int k = a[j]; k <= C; ++k) {
            m[k] = min(m[k], m[k - a[j]] + 1);
        }
    }

    if (m[C] == INF) {
        cout << -1 << endl;
    } else {
        cout << m[C] << endl;
    }
    return 0;
}