using System.Collections;
using System.ComponentModel;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;

internal class Program
{
    private const long mod = 998244353;

    
    public static void Main(string[] args)
    {
        var line= Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
        int L = line[0], n = line[1];
        int [] x= Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
        var dpup = mkar(2 * L + 1, 0);
        dpup[L] = 1;
        var dpdow = mkar(2 * L + 1, 0);
        void upd(int len)
        {
            var ndpup = mkar(2 * L + 1, 0);
            var ndpdow = mkar(2 * L + 1, 0);
            for (int i = 0; i <= 2 * L; i++)
            {
                if (dpup[i]>0)
                {
                    ndpup[i + len] = ndpdow[i + len] = 1;
                }

                if (dpdow[i] > 0)
                {
                    ndpup[i - len] = ndpdow[i - len] = 1;
                }
            }

            dpup = ndpup;
            dpdow = ndpdow;
        }

        for (int i = 0; i < n; i++)
        {
            int len = x[i];
            if (i > 0) len -= x[i - 1];
            upd(len);
        }

        int ans = L;
        int las = L - x[n - 1];
        for (int i = 0; i <= 2 * L; i++)
        {
            if (dpdow[i]>0)
            {
                int val = i - las;
                val -= L;
                val = Math.Abs(val);
                ans = Math.Min(ans, val);
            }
        }
        Console.WriteLine(ans);
    }

    public static List<int> mkar(int n, int val)
    {
        List<int> res = new List<int>(n);
        for(int i=0;i<n;i++)res.Add(val);
        return res;
    }
}