using System;
using System.Linq;

namespace No370_1{
    public class Program{
        public static void Main(string[] args){
            var sr = new StreamReader();
            //---------------------------------
            var n = sr.Next<int>();
            var m = sr.Next<int>();
            var dm = sr.Next<int>(m);

            n -= dm.Count(x => x == 0);

            if(n <= 0) {
                Console.WriteLine(0);
                return;
            }

            var pn = dm.Where(x => x >= 1).Concat(new[]{0}).OrderBy(x => x).ToArray();
            var mn = dm.Where(x => x <= -1).Concat(new[]{0}).Select(x => -x).OrderBy(x => x).ToArray();

            n++;
            var from = Math.Max(0, n - pn.Length);
            var to = Math.Min(n, mn.Length);

            var ans = int.MaxValue;
            for(var i = from; i < to; i++){
                for(var j = 0; j <= 1; j++){
                    ans = Math.Min(ans, pn[n - i - 1] * (1 + j) + mn[i] * (2 - j));
                }
            }

            Console.WriteLine(ans);
            //---------------------------------
        }
    }

    public class StreamReader{
        private readonly char[] _c = {' '};
        private int _index = -1;
        private string[] _input = new string[0];

        public T Next<T>(){
            if(_index == _input.Length - 1){
                _index = -1;
                while(true){
                    string rl = Console.ReadLine();
                    if(rl == null){
                        if(typeof(T).IsClass) return default(T);
                        return (T)typeof(T).GetField("MinValue").GetValue(null);
                    }
                    if(rl != ""){
                        _input = rl.Split(_c, StringSplitOptions.RemoveEmptyEntries);
                        break;
                    }
                }
            }
            return (T)Convert.ChangeType(_input[++_index], typeof(T), System.Globalization.CultureInfo.InvariantCulture);
        }

        public T[] Next<T>(int x){
            var result = new T[x];
            for(var i = 0; i < x; ++i){
                result[i] = Next<T>();
            }
            return result;
        }
    }
}