#include <cstdio>
#include <iostream>
#include <vector>
#include <map>
#include <set>
#include <string>
#include <cstring>
#include <sstream>
#include <algorithm>
#include <functional>
#include <queue>
#include <stack>
#include <cmath>
#include <iomanip>
#include <list>
#include <tuple>
#include <bitset>
#include <ciso646>

using namespace std;

inline bool cheak(int x, int y, int xMax, int yMax){ return x >= 0 && y >= 0 && xMax > x && yMax > y; }
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }
template<class T> inline T sqr(T x) { return x*x; }

typedef pair<int, int> P;
typedef tuple<int, int, int> T;
typedef long long ll;
typedef unsigned long long ull;

#define For(i,a,b)	for(int (i) = (a);i < (b);(i)++)
#define rep(i,n)	For(i,0,n)
#define clr(a)		memset((a), 0 ,sizeof(a))
#define mclr(a)		memset((a), -1 ,sizeof(a))
#define all(a)		(a).begin(),(a).end()
#define sz(a)		(sizeof(a))
#define Fill(a,v)	fill((int*)a,(int*)(a+(sz(a)/sz(*(a)))),v)

const int dx[8] = { 1, 0, -1, 0, 1, 1, -1, -1 }, dy[8] = { 0, -1, 0, 1, -1, 1, -1, 1 };
const int mod = 1000000007;
const int INF = 1e9;

ll c, n;
vector<ll> a;

ll memo[101][100001];
ll dfs(ll m,ll t){
	if (memo[m][t] != -1)
		return memo[m][t];
	ll ret = INF;
	if (m == n){
		if (t == c)
			return 0;
		else
			return INF;
	}
	for (ll x = 0;;x++){
		if (t + a[m] * x <= c){
			ret = min(ret,dfs(m + 1, t + a[m] * x) + x);
		}
		else break;
	}

	return memo[m][t] = ret;
}

int main()
{
	cin >> c >> n;
	rep(i, n){
		ll t;
		cin >> t;
		a.push_back(t);
	}
	mclr(memo);
	ll ans = dfs(0, 0);
	if (ans >= INF)ans = -1;
	cout << ans << endl;

	return 0;
}