#include <cstdio>
#include <cstring>
#include <iostream>
#include <string>
#include <cmath>
#include <bitset>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <deque>
#include <algorithm>
#include <complex>
#include <unordered_map>
using namespace std;
typedef long long int ll;
typedef pair<ll, int> Pl;
typedef pair<int, int> P;
const int INF=1e9;
int main()
{
	int c;
	cin>>c;
	int n;
	cin>>n;
	vector<int> a;
	for(int i=0; i<n; i++){
		int a0;
		cin>>a0;
		a.push_back(a0);
	}
	sort(a.begin(), a.end());
	a.erase(unique(a.begin(), a.end()), a.end());
	int dp[100001];
	fill(dp, dp+c+1, INF);
	dp[0]=0;
	for(int i=0; i<a.size(); i++){
		for(int j=0; j<=c-a[i]; j++){
			dp[j+a[i]]=min(dp[j+a[i]], dp[j]+1);
		}
	}
	if(dp[c]<INF) cout<<dp[c]<<endl;
	else cout<<-1<<endl;
	return 0;
}