using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Text;
using System.Text.RegularExpressions;
using System.Linq;
using System.IO;

class Program
{
    static void Main()
    {
        new Magatro().Solve();
    }
}

class Magatro
{
    private int C;
    private int N;
    private int[] A;
    private void Scan()
    {
        C = int.Parse(Console.ReadLine());
        N = int.Parse(Console.ReadLine());
        A = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
    }

    public void Solve()
    {
        Scan();
        var cost = (new int[C + 1]).Select(i => int.MaxValue).ToArray();
        cost[0] = 0;
        for (int i = 0; i <= C; i++)
        {
            if (cost[i] == int.MaxValue) continue;

            foreach (int j in A)
            {
                if (i + j <= C)
                {
                    cost[i + j] = Math.Min(cost[i + j], cost[i] + 1);
                }
            }
        }
        Console.WriteLine(cost[C] == int.MaxValue ? -1 : cost[C]);

    }
}