///solutie putin mai veche
#include <iostream>
#include <fstream>

using namespace std;

ifstream fin("secv2.in");
ofstream fout("secv2.out");

int sp[100002],minn[100002];

int main()
{
    int n,k;
    fin>>n>>k;
    for(int i=1;i<=n;i++)
    {
        fin>>sp[i];
        sp[i]+=sp[i-1];
        minn[i]=min(minn[i-1],sp[i]);
    }
    int rez=-2e9;
    for(int i=k;i<=n;i++)
    {
        rez=max(rez,sp[i]-minn[i-k]);
    }
    fout<<rez;
    return 0;
}