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

namespace Keses
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] inp1 = Console.ReadLine().Split().Select(int.Parse).ToArray();
            int[] inp2 = Console.ReadLine().Split().Select(int.Parse).ToArray();
            long loc;
            long locmax;
            long min = int.MaxValue;
            for (int i = inp1[1] - 1; i < inp1[0]; i++)
            {
                locmax = 0;
                loc = 0;
                for (int u = 0; u > -inp1[1]; u--)
                {
                    locmax = Math.Max(locmax, inp2[u + i] + u);
                    //Console.WriteLine("f" + locmax);
                }
                for (int u = 0; u > -inp1[1]; u--)
                {
                    loc += inp2[u + i] - (locmax - u);
                    //Console.WriteLine("g" + loc);
                }
                if (-loc < min)
                {
                    min = -loc;
                }
            }
            Console.WriteLine(min);
            Console.ReadLine();
        }
    }
}