#define _CRT_SECURE_NO_WARNINGS
#include "bits/stdc++.h"
#define rep(i,n) for(int i = 0;i < n;i++)
#define P(p) cout<<(p)<<endl;
using namespace std;
typedef long long ll;
int dx[] = { 0, 1, 0, -1 };
int dy[] = { -1, 0, 1, 0 };

int sttoi(std::string str) {
	int ret;
	std::stringstream ss; ss << str;
	ss >> ret;
	return ret;
}

ll gcd(ll a, ll b){
	if (b > a)swap(a, b); if (b == 0)return a; else{ return gcd(b, a%b); }
}

void solve() {
	int dp[100001];
	int c,n,A[100];
	cin >> c >> n;
	rep(i, n)cin >> A[i];

	rep(i, c+1)dp[i] = 1e9;

	dp[0] = 0;
	rep(i, c+1){
		rep(j, n){
			if (i - A[j] >= 0 && dp[i-A[j]] != 1e9){
				dp[i] = min(dp[i], dp[i - A[j]] + 1);
			}
		}
	}
	P(dp[c] != 1e9 ? dp[c] : -1);
}

int main() {
	solve();
	return 0;
}