#include <algorithm>
#include <array>
#include <sstream>
#include <cstdio>
#include <functional>
#include <cstdlib>
#include <cctype>
#include <ostream>
#include<complex>
#include <cmath>
#include <iostream>
#include <stack>
#include <fstream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <bitset>
#include <iomanip>
#include <string>
#include <vector>
#include <string>
using namespace std;
#define OB (bitset<32>)
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define ALLOF(c) begin(), (c),end()

typedef long long ll;

#define PI acos(-1)
#define EPS 0.000000001
#define MOD 1000000007



int main()
{  
    int c;
    int n;
    int a[100];
    cin >>c >> n;
    fill(a,a+100,-1);//invalid error on sort
    rep(i,n)
    {
        cin >> a[i];
    }
    map<int,int> dp[10001];
    dp[0].insert(make_pair(0,0));
    sort(a,a+100,greater<int>());
    rep(i,n)
    {
        for (auto ittr = dp[i].begin();  ittr != dp[i].end() ; ittr++)
        {
            for (int k = 0;; k++)
            {
                int x = ittr->first;
                int y = ittr->second;
                if ((x + k*a[i]) > c)
                {
                    break;
                }
                auto next = dp[i+1].find(x + k*a[i]);
                if (next == dp[i+1].end())
                {
                    dp[i+1].insert(make_pair(x +k*a[i],y+k));
                    continue;
                }
                if ( next->second > y+k)
                {
                    dp[i+1].erase(next->first);
                    dp[i+1].insert(make_pair(x+k*a[i],y+k));
                }
            }
        } 
    }
    if (dp[n].find(c) != dp[n].end())
    {
        int ans = dp[n].find(c)->second;
        cout << ans <<endl;
        return 0;
    }
    cout << "-1" << endl;
    return 0;
}