#include <iostream>
#include <cstdio>
#include <vector>

using namespace std;

const int INF = 1e7;

int main() {
	int c, n;

	cin >> c >> n;
	vector<int> a(n, 0);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}

	vector<int> dp(1e5 * 2 + 1, INF);
	dp[0] = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < c; j++) {
			if (dp[j] != INF) {
				dp[j + a[i]] = min(dp[j + a[i]], dp[j] + 1);
			}
		}
	}

	if (dp[c] == INF) {
		cout << -1 << endl;
	} else {
		cout << dp[c] << endl;
	}

	return 0;
}