#include <stdio.h>
#include <iostream>
using namespace std;

FILE*f=fopen("spargere2.in","r");
FILE*g=fopen("spargere2.out","w");
long long i,n,Smax,S,A[1000000],s[1000000],k,j;
int main()
{

    fscanf(f,"%lld%lld",&n,&k);
    for(i=1;i<=n;i++)
        fscanf(f,"%d",&A[i]);

    s[0]=0;
    for(i=1;i<=n;i++)
        {   if(A[i]>=0)
            s[i]=max(A[i]+s[i-k],max(s[i-1],A[i]));
            else s[i]=s[i-1];
        }

    if(s[n]<0) fprintf(g,"0");
        fprintf(g,"%lld",s[n]);

    fclose(f);
    fclose(g);
    return 0;
}