#include <cstdio>
#include <deque>
using namespace std;

int main()
{
   freopen("deque.in","r",stdin);
   freopen("deque.out","w",stdout);
   int n,k;
   scanf("%d%d",&n,&k);
   long long sum=0;
   deque<int>d;
   deque<int>poz;
   for(register int i=1;i<=n;i++)
   {
   	   int nr;
   	   scanf("%d",&nr);
   	   if(i<k)
	   {
	   	while(!d.empty())
	   {
	   	  if(d.back()> nr)d.pop_back(),poz.pop_back();
	   	  else
			break;
	   }
	   d.push_back(nr);
	   poz.push_back(i);
	   continue;
	   }
	   if(i>=k)
	   {
	   		   	while(!d.empty())
	   {
	   	  if(d.back()> nr)d.pop_back(),poz.pop_back();
	   	  else
			break;
	   }
	   d.push_back(nr);
	   poz.push_back(i);
	   	sum+=d.front();
	   	if(poz.front()==(i-k+1))
			d.pop_front(),poz.pop_front();
	   }
   }
   printf("%lld",sum);
    return 0;
}