#include <cstdio>
#include <iostream>
#include <algorithm>
#include <complex>
#include <queue>
#include <map>
#include <string>
using namespace std;

#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(b)-1;i>=(a);i--)
#define REP(i,n) for (int i=0;i<(n);i++)
#define RREP(i,n) for (int i=(n)-1;i>=0;i--)
#define pb push_back
#define ALL(a) (a).begin(),(a).end()

#define EPS (1e-10)
#define EQ(a,b) (abs((a)-(b)) < EPS)

#define PI 3.1415926535

typedef long long ll;
typedef pair<int, int> P;
//typedef complex<double> C;

const int INF = 99999999;
const int MAX_N = 100;
const int MAX_C = 100000;

int C, N;
int a[MAX_N];
int dp[MAX_C + 1];

void input() {
	cin >> C >> N;
	REP(i, N) cin >> a[i];
}

void solve() {
	REP(j, C + 1) dp[j] = INF;
	dp[0] = 0;
	REP(i, N) {
		REP(j, C + 1) {
			if (j + a[i] <= C) {
				dp[j + a[i]] = min(dp[j + a[i]], dp[j] + 1);
			}
		}
	}
	if (dp[C] >= INF) dp[C] = -1;
	cout << dp[C] << endl;
}

int main() {
	input();
	solve();
}