using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Task1787
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] kMinute = Console.ReadLine().Split(new char[] { ' ', '\t', '\n', '\r' }, StringSplitOptions.RemoveEmptyEntries);
            int k = int.Parse(kMinute[0]);
            int n = int.Parse(kMinute[1]);
            string[] nCam = Console.ReadLine().Split(new char[] { ' ', '\t', '\n', '\r' }, StringSplitOptions.RemoveEmptyEntries);
            int sum = 0;
            foreach (var item in nCam)
            {
                sum += int.Parse(item);
            }
            Console.WriteLine(sum - (k * n));
        }
    }
}