#include <stdio.h>
const int NR=5000001;
/*
int scrie(int p,int u,int d[],int v[])
{
	int i;
	for (i=p; i<=u; i++)
		printf("%d ",v[d[i]]);
	printf("\n");
}
*/
int v[NR],d[NR];
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	int n,k,i,p,u;
	long long s=0;
	scanf("%d%d",&n,&k);
	for (i=1; i<=n; i++)
		scanf("%d",&v[i]);
	p=1;u=0;
	d[++u]=1;
	for (i=2; i<=k; ++i)
	{
		while (u>=p && v[d[u]]>=v[i])
			--u;
		d[++u]=i;
		//scrie(p,u,d,v);
	}
	s=v[d[p]];
	//printf("%d\n",v[d[p]]); 
	for (i=k+1; i<=n; ++i)
	{
		while (p<=u && d[p]<i-k+1)
			++p;
		while(u>=p && v[d[u]]>=v[i])
			--u;
		d[++u]=i;
		s+=v[d[p]];
		//scrie(p,u,d,v);
		//printf("%d\n",v[d[p]]); 
	}
	printf("%lld\n",s);
	return 0;
}
/*
#include<stdio.h>

const int N=5000005;

int v[N],deq[N],p,u=-1,n,k;

void adaug(int i)
{
	while(u>=p && v[deq[u]]>=v[i])
		--u;
	deq[++u]=i;
}

void scot(int i)
{
	while(i-deq[p]>=k)
		++p;
}

long long calcul()
{
	int i;
	long long s=0;
	scanf("%d%d",&n,&k);
	for(i=0;i<k;++i)
	{
		scanf("%d",&v[i]);
		adaug(i);
	}
	s+=v[deq[p]];
	for(;i<n;++i)
	{
		scanf("%d",&v[i]);
		scot(i);
		adaug(i);
		s+=v[deq[p]];
	}
	return s;
}

int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	printf("%lld\n",calcul());
	return 0;
}
*/