#include<stdio.h>
#define maxn 5000001
int D[maxn],A[maxn],back,front,i,n,S,k;
int main ()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	front=1;
	back=0;
	for(i=1;i<=n;++i)
	{
		scanf("%d",&A[i]);
	}
	for(i=1;i<=n;++i)
	{
		while(front<=back&&A[i]<=A[D[back]]) --back;
		D[++back]=i;
		if(D[front]==i-k) ++front;
		if(i>=k) S+=A[D[front]];
	}
	printf("%lld",S);
	return 0;
}