#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint1000000007;
using namespace std;
#define rep(i,n) for(int i=0;i<(n);i++)
#define Inf 1000000000000001


int main(){
	int n,c;
	cin>>c>>n;
	
	vector<long long> dp(c+1,Inf);
	dp[0] = 0;
	vector<int> a(n);
	rep(i,n)cin>>a[i];
	
	rep(i,n){
		rep(j,c+1){
			if(j-a[i]<0)continue;
			dp[j] = min(dp[j], dp[j-a[i]]+1);
		}
	}
	long long ans = dp.back();
	if(ans==Inf)ans = -1;
	cout<<ans<<endl;
	
	return 0;
}