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

namespace Contest
{
    class Program
    {
        static void Main(string[] args)
        {
            AGC008.B();
        }

        class AGC008
        {
            public static void A()
            {
                var X = Read.Int();
                var Y = Read.Int();
                var AX = Math.Abs(X);
                var AY = Math.Abs(Y);
                if (AX == AY)
                {
                    Console.WriteLine(1);
                }
                else if (AX < AY)
                {
                    Console.WriteLine(AY - AX + (X < 0 ? 1 : 0) + (Y < 0 ? 1 : 0));
                }
                else
                {
                    Console.WriteLine(AX - AY + (X > 0 ? 1 : 0) + (Y > 0 ? 1 : 0));
                }
            }
            public static void B()
            {
                var N = Read.Int();
                var K = Read.Long();
                var A = Read.LongN();
                var Asum = new long[N + 1];
                var Bsum = new long[N + 1];
                for(int i = 0; i < N; ++i)
                {
                    Asum[i + 1] = Asum[i] + A[i];
                    Bsum[i + 1] = Bsum[i] + Math.Max(0, A[i]);
                }
                long max = 0;
                for(int i = 0; i < N - K + 1; ++i)
                {
                    long score = Bsum[i] - Bsum[0] + Math.Max(0, Asum[i + K] - Asum[i]) + Bsum[N] - Bsum[i + K];
                    max = Math.Max(max, score);
                }
                Console.WriteLine(max);
            }
            public static void C()
            {
                var A = Read.LongN();
                var AI = A[0];
                var AO = A[1];
                var AJ = A[3];
                var AL = A[4];
                var K1 = AI / 2 * 2 + AO + AJ / 2 * 2 + AL / 2 * 2;
                var K2 = AI > 0 && AJ > 0 && AL > 0 ? (AI - 1) / 2 * 2 + AO + (AJ - 1) / 2 * 2 + (AL - 1) / 2 * 2 + 2 : 0;
                Console.WriteLine(Math.Max(K1, K2));
            }
        }


        class Util
        {
        }

        static class Read
        {
            static Queue<string> queue = new Queue<string>();
            static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
            public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
            public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
            public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
            public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
            public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
            public static string[] StrN() { return Console.ReadLine().Split(' '); }
            public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
            public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
            public static long[,] LongMatrix(int r, int c)
            {
                var mat = new long[r, c];
                for (int i = 0; i < r; ++i)
                {
                    var x = Read.LongN();
                    for (int j = 0; j < c; ++j)
                    {
                        mat[i, j] = x[j];
                    }
                }
                return mat;
            }
            public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M)
            {
                Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new HashSet<int>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1]);
                    dict[ab[1]].Add(ab[0]);
                }
                return dict;
            }
            public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
            {
                Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>();
                for (int i = 0; i <= N; ++i)
                {
                    dict.Add(i, new Dictionary<int, long>());
                }
                for (int i = 0; i < M; ++i)
                {
                    var ab = Read.IntN();
                    dict[ab[0]].Add(ab[1], ab[2]);
                    dict[ab[1]].Add(ab[0], ab[2]);
                }
                return dict;
            }
        }
    }
}


Measured memory_bytes: 32092