using System;
using System.Collections.Generic;
using System.Linq;

namespace No198
{
	class MainClass
	{
		private static long Calculate(long target, long[] values)
		{
			return values.Sum (v => Math.Abs (target - v));
		}

		public static void Main (string[] args)
		{			
			var b = Convert.ToInt64(Console.ReadLine ());
			var n = Convert.ToInt32 (Console.ReadLine ());
			long[] data = new long[n];
			for (int i = 0; i < n; i++) {
				data [i] = Convert.ToInt64 (Console.ReadLine ());
			}
			var sum = data.Sum () + b;
			var maxValue = sum / n;
			var minValue = data.Min ();
			var midValue = (maxValue + minValue) / 2L;

			var min = long.MaxValue;

			do {
				var maxOperation = Calculate (maxValue, data);
				var minOperation = Calculate (minValue, data);
				var midOperation = Calculate (midValue, data);
				min = Math.Min (min, maxOperation);
				min = Math.Min (min, minOperation);
				min = Math.Min (min, midOperation);

				if (maxOperation > minOperation) {
					maxValue = (midValue + maxValue) / 2;
					midValue = (maxValue + minValue) / 2;
				} else {
					minValue = (midValue + minValue) / 2;
					midValue = (maxValue + minValue) / 2;
				}
			} while (maxValue - midValue > 1 && midValue - minValue > 1);
			{
				var maxOperation = Calculate (maxValue, data);
				var minOperation = Calculate (minValue, data);
				var midOperation = Calculate (midValue, data);
				min = Math.Min (min, maxOperation);
				min = Math.Min (min, minOperation);
				min = Math.Min (min, midOperation);
			}
			Console.WriteLine (min.ToString ());
		}
	}
}