#include<fstream.h>
#define max 6000000

 ifstream fi("deque.in");
 ofstream g("deque.out");
  long long a[max],i,f,b,k,n,d[max];
  long long sum;
int main()
{
 fi>>n>>k;
 for(i=1;i<=n;i++)
   fi>>a[i];
 f=1;
 b=0;
 for(i=1;i<=n;i++)
 {
  while(f<=b && a[i]<=a[d[b]])
    b--;
  d[++b]=i;
  if(d[f]==i-k) f++;
  if(i>=k) sum+=a[d[f]];
 }

 g<<sum;

 return 0;
}