#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("ferma.in");
ofstream fout("ferma.out");

int N, K, Sp[10002], sumamax = -100000;

void Citire()
{
    int nr;

    fin >> N >> K;

    Sp[0] = 0;

    for (int i = 1; i <= N; i++)
        fin >> nr, Sp[i] = Sp[i - 1] + nr;

    for (int i = 1; i + K - 1 <= N; i++)
    {
        if (sumamax < Sp[i + K - 1] - Sp[i - 1])
            sumamax = Sp[i + K - 1] - Sp[i - 1];
        if (sumamax < Sp[i - 1] - Sp[i + K - 1]);
    }
}

void Rezolvare()
{
    if (sumamax > 0)
        fout << sumamax * K;
    else
        fout << 0;
}

int main()
{
    Citire();

    Rezolvare();

    return 0;
}