#include <bits/stdc++.h>

using namespace std;

const int INF = 1e9;

int dp[100010];

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