#include<cstdio>
int n,k,st,dr,a[5000001],dq[5000001];
long long s;
inline void elimst(int i)
{
	if(i-dq[st]==k)
		++st;
}
void elimdr(int i)
{
	while(st<=dr&&a[dq[dr]]>=a[i])
		--dr;
	dq[++dr]=i;
}
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	s=0; st=0; dr=0;
	for(int i=1;i<=k;++i)
	{
		scanf("%d",&a[i]);
		elimst(i);
		elimdr(i);
	}
	s=a[dq[st]];
	for(int i=k+1;i<=n;++i)
	{
		scanf("%d",&a[i]);
		elimst(i);
		elimdr(i);
		s+=a[dq[st]];
	}
	printf("%lld\n",s);
	return 0;
}