#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <climits>
#include <vector>
#include <numeric>
#include <complex>
#include <map>
#include <bitset>
using namespace std;

//#define __int64 long long
#define long __int64
#define REP(i,a,b) for(int i=a;i<b;i++)
#define rep(i,n) REP(i,0,n)
const int Vecy[4] = {0,-1,0,1};
const int Vecx[4] = {1,0,-1,0};


int main(){
	int dp[100001];
	int total,n;
	int a[100];
	for(int i=0; i<100001; i++){
		dp[i] = INT_MAX-1;
	}
	dp[0] = 0;
	
	cin >> total >> n;
	rep(i,n){
		cin >> a[i];
	}
	
	sort(a, a + n, greater<int>());  	//降順
	
	//dp
	for(int i=0; i<n; i++){
		for(int dpi=0; dpi<=total; dpi++){
			if(dp[i] != INT_MAX){
				if(dpi + a[i] <= total){
					dp[dpi + a[i]] = min(dp[dpi + a[i]], dp[dpi] + 1);
					//cout << "dp[" << dpi + a[i] << "] = " << dp[dpi + a[i]] << endl;
				}
			}
		}
	}
	
	cout << (dp[total] == INT_MAX-1 ? -1 : dp[total])  << endl;
	
    return 0;
}