#include <bits/stdc++.h>

using namespace std;

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    const int INF = 1000000;
    int c, n, a[100];
    cin >> c >> n;
    vector< vector<int> > dp(n + 1, vector<int>(c + 1, INF));
    for(int i = 0; i < n; i++){
        cin >> a[i];
        dp[i][0] = 0;
    }
    dp[n][0] = 0;
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j < a[i - 1]; j++) {
            dp[i][j] = dp[i - 1][j];
        }
        for(int j = a[i - 1]; j <= c; j++) {
            dp[i][j] = min(dp[i - 1][j], dp[i][j - a[i - 1]] + 1);
        }
    }
    if (dp[n][c] == INF) cout << -1 << "\n";
    else cout << dp[n][c] << "\n";
    return 0;
}