#include <iostream>
#include <vector>
#include <climits>
using namespace std;

int main() {
	int c, n;
	cin >> c >> n;

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

	vector<int> dp(c + 1, INT_MAX);
	dp[0] = 0;

	for (int a : constants) {
		for (int i = 0; i <= c - a; i++) {
			if (dp[i] < INT_MAX && dp[i + a] > dp[i] + 1) {
				dp[i + a] = dp[i] + 1;
			}
		}
	}

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

	return 0;
}