#include<cstdio>
#include<algorithm>
#define NM 5000010 
using namespace std;

int n,k,x,p,nmax=0;
long long s=0;
pair< int,int > heap[NM],aux;

inline void coboara(int nod)
{
    while( nod*2+1<=nmax && ( heap[nod].first >= heap[nod*2].first || heap[nod].first >= heap[nod*2+1].first ) )
        if(heap[nod*2+1].first<heap[nod*2].first) 
		{
			swap(heap[nod],heap[nod*2+1]);
			nod=nod*2+1;
		}
		else 
		{
			swap(heap[nod],heap[nod*2]);
			nod=nod*2;
		}
    if(nod*2==nmax && heap[nod].first >= heap[nod*2].first)
        swap(heap[nod],heap[nod*2]);
}
int main()
{
    freopen("deque.in","rt",stdin);
    freopen("deque.out","wt",stdout);
    scanf("%d%d",&n,&k);
	
	for(register int i=1;i<k;i++)
	{
		scanf("%d",&aux.first);
		aux.second=i;
		heap[++nmax]=aux;
		while(nmax>1 && heap[nmax].first <= heap[nmax/2].first)
		{
			swap(heap[nmax],heap[nmax/2]);
			nmax/=2;
		}
	}
    for(register int i=k;i<=n;++i)
    {
        scanf("%d",&aux.first);
		
        while(nmax>0 && ( ( heap[1].second <= i-k ) || (heap[1].first >= aux.first) ))
		{
			heap[1]=heap[nmax--];
			coboara(1);
		}
		aux.second=i;
		heap[++nmax]=aux;
		while(nmax>1 && heap[nmax].first <= heap[nmax/2].first)
		{
			swap(heap[nmax],heap[nmax/2]);
			nmax/=2;
		}
        s+=heap[1].first;
    }
    printf("%lld\n",s);
    return 0;
}