#include <bits/stdc++.h>
using namespace std;

const int INF = 1 << 28;

int c, n;
int a[100];
int dp[100001];

int main()
{
	cin >> c >> n;
	for (int i = 0; i < n; i++){
		cin >> a[i];
	}
	
	fill_n(dp, 100001, INF);
	dp[0] = 0;
	
	for (int i = 0; i < n; i++){
		for (int j = 0; j + a[i] <= c; j++){
			dp[j + a[i]] = min(dp[j + a[i]], dp[j] + 1);
		}
	}
	
	cout << (dp[c] != INF ? dp[c] : -1) << endl;
}