#include<cstdio>
int k,n,st,dr,v[5000010],dq[5000010];
inline void stanga (int i)
{
	if(i-dq[st]==k)
		++st;
}
void dreapta(int i)
{
	while(st<=dr&&v[dq[dr]]>=v[i])
		--dr;
	dq[++dr]=i;
}

int main()
{
	int i;
	long long s;
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	st=dr=0;
	for(i=1;i<=k;i++)
	{
		scanf("%d",&v[i]);
		dreapta(i);
	}	
	s=v[dq[st]];	
	for(i=k+1;i<=n;i++)
	{
		scanf("%d",&v[i]);
		stanga(i);
		dreapta(i);
		s+=v[dq[st]];
	}
	printf("%lld",s);
	return 0;
}