#include <fstream>
using namespace std;

int n,k,a[5000000];
int p[5000000];
int st,dr,i;
long long s;

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]);
	st=1;
	dr=0;
	for (i=1;i<=n;i++)
	{
		while ((st<=dr)&&(a[i]<=a[p[dr]]))
			dr--;
		p[++dr]=i;
		if (p[st]==i-k)
			st++;
		if (i>=k)
			s+=a[p[st]];
	}
	printf("%lld\n",s);
	return 0;
}