#include <cstdlib>
#include <cmath>
#include <climits>
#include <cfloat>
#include <map>
#include <set>
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <sstream>
#include <complex>
#include <stack>
#include <queue>
#include <cstdio>
#include <cstring>
#include <iterator>
#include <bitset>
#include <unordered_set>
#include <unordered_map>
#include <fstream>
#include <iomanip>
//#include <utility>
//#include <memory>
//#include <functional>
//#include <deque>
//#include <cctype>
//#include <ctime>
//#include <numeric>
//#include <list>
//#include <iomanip>

//#if __cplusplus >= 201103L
//#include <array>
//#include <tuple>
//#include <initializer_list>
//#include <forward_list>
//
//#define cauto const auto&
//#else

//#endif

using namespace std;


typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;

typedef vector<int> vint;
typedef vector<vector<int> > vvint;
typedef vector<long long> vll, vLL;
typedef vector<vector<long long> > vvll, vvLL;

#define VV(T) vector<vector< T > >

template <class T>
void initvv(vector<vector<T> > &v, int a, int b, const T &t = T()){
    v.assign(a, vector<T>(b, t));
}

template <class F, class T>
void convert(const F &f, T &t){
    stringstream ss;
    ss << f;
    ss >> t;
}

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define reep(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n) reep((i),0,(n))
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define F first
#define S second
#define mkp make_pair
#define RALL(v) (v).rbegin(),(v).rend()
#define DEBUG
#ifdef DEBUG
#define dump(x)  cout << #x << " = " << (x) << endl;
#define debug(x) cout << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;
#else
#define dump(x) 
#define debug(x) 
#endif
#define LDcout(x,n) fixed<<setprecision(n)<<x

#define MOD 1000000007LL
#define EPS 1e-8
static const int INF=1<<24;
int dp[100010];
int foo(int a,int b){
	if(a%b==0){
		return a/b;
	}
	if(a<b){
		return dp[a];
	}
	if(dp[a-b]==INF){
		return INF;
	}
	int l=1;
	int r=a/b;
	if(dp[a-r*b]!=INF){
		return dp[a-r*b];
	}
	while(l-r>1){
		int mid=(r+l)/2;
		if(dp[mid]==INF){
			r=mid;
		}
		else{
			l=mid;
		}
	}
	return dp[a-l*b]+l;
}
void mainmain(){
	int C;
	cin>>C;
	int n;
	cin>>n;
	vint a(n);
	rep(i,n) cin>>a[i];
	sort(ALL(a));
	rep(i,100010) dp[i]=INF;
	dp[0]=0;
	rep(i,n){
		rep(j,100010){
			int t=foo(j,a[i]);
			dp[j]=min(dp[j],t);
		}
	}
	if(dp[C]==INF) cout<<-1<<endl;
	else cout<<dp[C]<<endl;
}


signed main() {
	ios_base::sync_with_stdio(false);
  	cout<<fixed<<setprecision(20);
    mainmain();
}