#include<fstream>
#define inf 100000005
#define dim 50000000
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
long a[dim],b[dim];
int i,j,k,p,nr,n,s;
int rez,minn;
int main()
{
	f>>n>>k;
	for(i=1;i<=n;i++)
		f>>a[i];
	rez=inf;
	for (i=1;i<=n;i++)
	{
		if (a[i]<=rez)
		{
			rez=a[i];
			p=i;
		}
		if(p<=i-k)
		{
			rez=inf;
			p=0;
			for (j=0;j<k;j++)
				if (a[i-j]<=rez) 
					{
						rez=a[i-j];
						p=i-j;
				}
		}
		if (i>=k)
			s+=rez;
	}
	g<<s;
	return 0;
}