#include <bits/stdc++.h>
#include <atcoder/modint>
using namespace std;
using mint = atcoder::static_modint<(int)1e9 + 7>;
template <class F> class y_combinator {
	F f;

  public:
	y_combinator(F&& f) : f(std::forward<F>(f)) {}
	template <class... Args> auto operator()(Args &&... args) const { return f(*this, std::forward<Args>(args)...); }
};
using ll = long long;
using ld = long double;
template <class T, class U = std::less<T>> using prique = std::priority_queue<T, std::vector<T>, U>;
template <class T> T floor(T a, T b) { return a / b - (a % b && (a ^ b) < 0); }
template <class T> T ceil(T a, T b) { return floor(a + b - 1, b); }
template <class T> bool chmin(T& x, const T& y) { return (x > y ? x = y, true : false); }
template <class T> bool chmax(T& x, const T& y) { return (x < y ? x = y, true : false); }
#define overload4(a, b, c, d, e, ...) e
#define rep1(a) for (long long _i = 0; _i < (a); _i++)
#define rep2(i, a) for (long long i = 0; i < (a); i++)
#define rep3(i, a, b) for (long long i = (a); i < (b); i++)
#define rep4(i, a, b, c) for (long long i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep(i, a, b, c) for (long long i = (a); i > (b); i += (c))
#define all(x) std::begin(x), std::end(x)
#define rall(x) std::rbegin(x), std::rend(x)
#define pb push_back

void run_case() {
	int C, N;
	cin >> C >> N;
	vector<int> A(N);
	rep(i, N) cin >> A[i];
	sort(all(A));
	vector<pair<int,int>> B;
	for(int i = 0; i < N; ) {
		int j = i;
		while(j < N && A[i] == A[j]) j++;
		B.pb({A[i], j - i});
		i = j;
	}
	vector<int> dp(C+1, 1e9);
	dp[0] = 0;
	for(auto[a,cnt]:B) {
		vector<int> ndp(C+1,1e9);
		rep(y, 0, C+1) if(dp[y] != 1e9) {
			rep(x, 0, C/a+1) {
				if(!(x<=C/a/cnt)) break;
				if(x*a*cnt>C-y) break;
				int& cur = ndp[x*a*cnt+y];
				cur = min<int>(cur, dp[y]+x);
			}
		}
		swap(dp, ndp);
		//for(int i = 0; i < C+1; i++) cout << dp[i] << " \n"[i==C];
	}
	cout << (dp[C]==1e9?-1:dp[C]) << endl;
}

int main() {
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(nullptr);
	std::fixed(std::cout).precision(16);
	int T = 1;
	//cin >> T;
	while(T--) run_case();
	return 0;
}