//#define _GLIBCXX_DEBUG
#include <bits/stdc++.h>
#define rep(i, n) for(int i=0; i<n; ++i)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
using namespace std;
using ll = int64_t;
using ld = long double;
using P = pair<int, int>;
using vs = vector<string>;
using vi = vector<int>;
using vvi = vector<vi>;
template<class T> using PQ = priority_queue<T>;
template<class T> using PQG = priority_queue<T, vector<T>, greater<T> >;
const int INF = 100010001;
const ll LINF = (ll)INF*INF*10;
template<typename T1, typename T2>
inline bool chmax(T1 &a, T2 b) {return a < b && (a = b, true);}
template<typename T1, typename T2>
inline bool chmin(T1 &a, T2 b) {return a > b && (a = b, true);}
template<typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second;}
template<typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << ' ' << p.second;}

const int N = 100010;

//head

int c, n;
int a[110];
int dp[N];

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);
	cin >> c >> n;
	rep(i, n) cin >> a[i];

	fill(dp+1, dp+c+1, INF);
	rep(i, n) {
		rep(j, c-a[i]+1) {
			chmin(dp[j+a[i]], dp[j]+1);
		}
	}

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