#include <cstdio>
long long s;
int st,dr,n,k,i,min;
int a[5000001],dq[5000001];
inline void stanga(int i)
{
	if (dq[st]==i-k)
		st=st+1;
}
void dreapta (int i)
{
	while  (st<=dr && a[i]<=a[dq[dr]])
		dr=dr-1;
	dq[++dr]=i;
}
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]);
	s=0;
	for (i=1;i<=k-1;i++)
		dreapta(i);
	for (i=k;i<=n;i++)
	{
		stanga(i);
		dreapta(i);
		s+=a[dq[st]];
	}
	printf("%lld",s);
	return 0;
}