#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
 unsigned long long int * costs,*effectivecosts;
     int * status;
int end=0, n=0,k=0;;
//calculate effectivity
    void effectivity(){
    end=1;
        int i=0;
        for(i=0;i<n;i++)
     {   int g=i-k,h=i+k;
    if(g<0)
        g=0;
    if(h>=n)
        h=n-1;
    for(g;g<=h;g++){
      if(status[g]==1)
          {
 end=0;
          effectivecosts[i]+=costs[g]; 
    }
    }
    }
    }

int getMax()
    {
    int max=effectivecosts[0],i=0,pivot=0;
    for(i=0;i<n;i++)
{
        if(max<effectivecosts[i])
        {    max=effectivecosts[i];
         pivot=i;
        }
    }
   return pivot;
  
    
    
}

int main() {
  
    scanf("%d %d",&n ,&k);
     costs=(  unsigned long long int *)malloc(n*sizeof(  unsigned long long int ));
      status=(   int *)malloc(n*sizeof(  int ));
    effectivecosts=(  unsigned long long int *)malloc(n*sizeof(  unsigned long long int ));
    
    //initilaize
int i=0;
    for(i=0;i<n;i++)
        {status[i]=1;
        scanf("%lld",&costs[i]);
         effectivecosts[i]=0;
    }
   //  printf("%llu",costs[0]);
       
   // return 0;
    unsigned long long int tcosts=0;
    while(end==0)
{effectivity();
 if(end!=0)
     break;
 int max=getMax();
tcosts+=costs[max];
   int g=max-k,h=max+k;
    if(g<0)
        g=0;
    if(h>=n)
        h=n-1;
    for(g;g<=h;g++)
       status[g]=0;  

    }
    
    printf("%llu",tcosts);
    /* Enter your code here. Read input from STDIN. Print output to STDOUT */    
    return 0;
}