#include <bits/stdc++.h>

using namespace std;

#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define REP(i,n) FOR(i,0,n)
#define ALL(v) (v).begin(),(v).end()

template<typename A, typename B> inline bool chmax(A &a, B b) { if (a<b) { a=b; return 1; } return 0; }
template<typename A, typename B> inline bool chmin(A &a, B b) { if (a>b) { a=b; return 1; } return 0; }

typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<pii, pii> P;

const ll INF = 1ll<<29;
const ll MOD = 1000000007;
const double EPS  = 1e-10;

int c, n, a[100];
int dp[112345];

int main() {
	cin >> c >> n;
	REP(i, n) scanf("%d", a + i);
	
	fill(dp, dp + c + 1, INF);
	
	dp[0] = 0;
	REP(i, c + 1) {
		REP(j, n) {
			if (i + a[j] > c) continue;
			chmin(dp[i + a[j]], dp[i] + 1);
		}
	}
	
	if (dp[c] == INF) puts("-1");
	else cout << dp[c] << endl;
	
	return 0;
}