#include <bits/stdc++.h>

using namespace std;

int main() {
    const int INF = 1e9;
    int dp[100000 + 5];
    int c, n;

    cin >> c >> n;

    for (int i = 0; i <= c; i++) {
        dp[i] = INF;
    }
    dp[0] = 0;

    for (int i = 0; i < n; i++) {
        int a;
        cin >> a;
        for (int j = 0; j <= c; j++) {
            if (dp[j] == INF || j + a > c) {
                continue;
            }
            dp[j + a] = min(dp[j + a], dp[j] + 1);
        }
    }

    cout << (dp[c] == INF ? -1 : dp[c]) << endl;

    return 0;
}