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

using namespace std;

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

int a[50000001],c[50000001],i,p,u,k,n;
long long s;

int main()
{
    fscanf(f,"%d%d",&n,&k);
    for (i=1;i<=n;i++)
         fscanf(f,"%d",&a[i]);
         p=1;
         u=0;
    for (i=1; i<=n ; i++)
     {
         while (p<=u && a[i]<a[c[u]]) u--;
         c[++u]=i;

         if (c[p]==i-k) p++;
          if (i>=k)  s=(long long)s+a[c[p]];

     }

    fprintf(g,"%lld",s);

    fclose;
    return 0;
}