#include <iostream>
#include <vector>
using namespace std;
const int INF = 1000000;
int main(){
	int C;
	cin >> C;
	int N;
	cin >> N;
	vector<int> a(N);
	for (int i = 0; i < N; i++){
		cin >> a[i];
	}
	vector<int> dp(C + 1, INF);
	dp[0] = 0;
	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);
		}
	}
	if (dp[C] == INF){
		cout << -1 << endl;
	} else {
		cout << dp[C] << endl;
	}
}