#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;
}