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

namespace РџРѕРІРѕСЂРѕС‚
{
    class Program
    {
        static void Main(string[] args)
        {
            string[] mas = Console.ReadLine().Split(' ');
            int k = int.Parse(mas[0]);
            int n = int.Parse(mas[1]);
            int[] A = Console.ReadLine().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries).Select(i => int.Parse(i)).ToArray();
            int M = 0;
            for (int i = 0; i < n; i++)
            {
                M += A[i];
                if (M - k >= 0)
                {M -= k;}
                else
                {M = 0;}
            }
            Console.WriteLine(M);
        }
    }
}
Надеюсь понятно всё.