#include "bits/stdc++.h"
using namespace std;
#ifdef _DEBUG
#include "dump.hpp"
#else
#define dump(...)
#endif

//#define int long long
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(c) begin(c),end(c)
const int INF = sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = 1'000'000'007;
template<class T> bool chmax(T &a, const T &b) { if (a < b) { a = b; return true; } return false; }
template<class T> bool chmin(T &a, const T &b) { if (b < a) { a = b; return true; } return false; }

signed main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int C; cin >> C;
	int N; cin >> N;
	vector<int> a(N); rep(i, 0, N) {
		cin >> a[i];
	}
	vector<int> dp(C + 1, INF);
	dp[0] = 0;
	rep(i, 0, N) {
		rep(j, 0, C) {
			if (j + a[i] > C)break;
			chmin(dp[j + a[i]], dp[j] + 1);
		}
	}
	cout << (dp[C] == INF ? -1 : dp[C]) << endl;
	return 0;
}