using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;
using System.Globalization;
using static System.Console;
using Pair = System.Collections.Generic.KeyValuePair<int, int>;

class Program
{
    static void Main()
    {
        var sw = new StreamWriter(OpenStandardOutput()) { AutoFlush = false };
        SetOut(sw);
        new Program().solve();
        Out.Flush();
    }
    Scanner cin = new Scanner();
    readonly int[] dd = { 0, 1, 0, -1, 0 };
    readonly int mod = 1000000007;
    readonly string alfa = "abcdefghijklmnopqrstuvwxyz";

    int N, K;
    void solve()
    {
        N = cin.nextint;
        K = cin.nextint;
        var A = cin.scanint;

     
        long MAX = 0;
        for (int i = 0; i < N; i++)
        {
            MAX += Math.Max(0, A[i]);
        }
      
        long syakuB = 0;

        long syakuW = 0;


        for (int i = 0; i < K; i++)
        {
            if (A[i] < 0)
            {
                syakuB += A[i];
            }
            else
            {
                syakuW += -1 * A[i];
            }  
        }


        //WriteLine(syakuB + " " + syakuW);

        long syakuBnow = syakuB;
        long syakuWnow = syakuW;

        for (int l = 0; l + K < N ; l++)
        {
            if (A[l] < 0)
            {
                syakuBnow -= A[l];
            }
            else
            {
                syakuWnow -= -1 * A[l];
            }

            if (A[l + K] < 0)
            {
                syakuBnow += A[l + K];
            }
            else
            {
                syakuWnow += -1 * A[l + K];
            }
            syakuB = Math.Max(syakuB, syakuBnow);
            syakuW = Math.Max(syakuW, syakuWnow);
        }
        WriteLine(MAX + Math.Max(syakuB, syakuW));


        /*long syakunow = syakumax;

        for (l = 1; l + K <= N; l++)
        {
            syakunow = syakunow + A[l + K - 1] - A[l - 1];
            if (syakunow > syakumax)
            {
                syakumax = syakunow;
                syakuMaxP = l;
            }
            if (true)
            {

            }
        }
        for (l = 0; l + K <= N; l++)
        {
            long cnt = 0;
            long zone = 0;
            for (int i = 0; i < N; i++)
            {
                if (l <= i && i < l + K)
                {
                    zone += A[i];
                }
                else
                {
                    cnt += Math.Max(0, A[i]);
                }
            }
            ans = Math.Max(ans, cnt + Math.Max(0, zone));
        }*/




    }

}

class Scanner
{
    string[] s; int i;
    char[] cs = new char[] { ' ' };
    public Scanner() { s = new string[0]; i = 0; }
    public string[] scan { get { return ReadLine().Split(); } }
    public int[] scanint { get { return Array.ConvertAll(scan, int.Parse); } }
    public long[] scanlong { get { return Array.ConvertAll(scan, long.Parse); } }
    public double[] scandouble { get { return Array.ConvertAll(scan, double.Parse); } }
    public string next
    {
        get
        {
            if (i < s.Length) return s[i++];
            string st = ReadLine();
            while (st == "") st = ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            i = 0;
            return next;
        }
    }
    public int nextint { get { return int.Parse(next); } }
    public long nextlong { get { return long.Parse(next); } }
    public double nextdouble { get { return double.Parse(next); } }
}

Measured memory_bytes: 17240