#include <iostream>
#include <cmath>
#include <algorithm>
#include <math.h>
#include <vector>
#include <fstream>

using namespace std;
void Backtracking(int NCoin);

static int CoinsSet[16];
static int N, M;
static vector<int> coins;
static int a[17];

static int MinAmount = 1000000001, CurAmount;
static int Sum = 0;

int AmountCoins(int A[])
{
    MinAmount = M + M + 1;
    CurAmount = 0;
    Sum = 0;
    Backtracking(1);
    //if (MinAmount > M + M)
    //    MinAmount = 0;
    return MinAmount;

}

void Backtracking(int NCoin)
{
    if (NCoin > M) return;
    if (Sum > N) return;

    for (int i = 0; i <= 2; i++)
    {
        if (Sum == N)
        {
            if (CurAmount < MinAmount)
                MinAmount = CurAmount;
        }
        Backtracking(NCoin + 1);
        CurAmount++;
        Sum += Sum + a[NCoin];
    }
    CurAmount -= 3;
    Sum -= 3*a[NCoin];

}

int main()
{

    int Summ = 0;
    cin >> N >> M;

    for (int i = 0; i < M; ++i) {
        cin >> a[i];
        Summ += a[i];
    }

    if (Summ + Summ < N) {
        cout << "-1";
    } else {
        cout << AmountCoins(a);;
    }


    return 0;
}