#include <iostream>
#include <stdio.h>

using namespace std;

FILE *f=fopen("secv2.in","r");
FILE *g=fopen("secv2.out","w");

int mn,n,k,mx,sol,nr,i,a,sum[50005],best[50005];

int main()
{
    mx=-1260000000;
    fscanf(f,"%d%d",&n,&k);
    nr=0;
    sum[0]=0;
    for(i=1;i<=n;i++)
    {
        fscanf(f,"%d",&a);
        sum[i]=sum[i-1]+a;
    }
    mn=sum[1];
    best[0]=0;
    best[1]=1;
    for(i=2;i<=n;i++)
    {
        if(sum[i]<mn)mn=sum[i];
        best[i]=mn;
    }
    for(i=k;i<=n;i++)
        if(sum[i]-best[i-k]>mx)mx=sum[i]-best[i-k];

    fprintf(g,"%d",mx);
    fclose(g);
    return 0;
}