#include <iostream.h>
#include<fstream.h>

int deq[5000001],v[5000001];
int main()
{
	 int st=1,dr=0,n,i,k;
	 long long s=0;
	 ifstream g("date.in");
	 ofstream h("date.out");
	 f>>n>>k;
	 for(i=1;i<=n;i++)
		  f>>v[i];

  for(i=1;i<=n;i++){
		  while(st<=dr && v[deq[dr]]>=v[i])
						  dr--;
		  deq[++dr]=i;
		  while(deq[st]<=i-k)
						  st++;
		  if(i>=k)
				s+=v[deq[st]];
	 }
	 h<<s;
	 return 0;
}