#include<fstream>
using namespace std;
int n,i,j,k,a[5000010],deque[5000010],front,back;
long long suma;
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;++i)
		scanf("%d",&a[i]);
	front=1;
	back=0;
	for(i=1;i<=n;++i)
	{
		while(front<=back&&a[i]<a[deque[back]])
			back--;
		
		deque[++back]=i;
		
		if(deque[front]==i-k)
			++front;
		
		if(i>=k)
			suma+=a[deque[front]];
	}
	
	printf("%lld",suma);
	fclose(stdin);
   fclose(stdout);

	return 0;
}