#include<stdio.h>
const int N=5000001;
int d[N],v[N],n,k,st=1,dr,i;
long long s;
inline void stanga(int i)
{
	if(i-d[st]==k)
		++st;
}
inline void dreapta(int i)
{
	while(st<=dr && v[d[dr]]>=v[i])
		dr--;
}
inline void adauga(int i)
{
	d[++dr]=i;
}
int main()
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	scanf("%d%d",&n,&k);
	for(i=1;i<=n;i++)
		scanf("%d",&v[i]);
	for(i=1;i<=k;i++)
	{
		dreapta(i);
		adauga(i);
	}
	s=v[d[st]];
	for(;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		s = s+v[d[st]];
	}
	printf("%lld\n",s);
	return 0;
}