#include<stdio.h>

#define N 5000001

int n,dq[N],v[N],u,p,k;

long long s;

void citire()
{
	scanf("%d%d",&n,&k);
	for(int i=0;i<n;++i)
		scanf("%d",&v[i]);
}

void dreapta(int i)
{
	while(u!=p && v[dq[u-1]]>=v[i])
		u--;
	dq[u++]=i;
}

void stanga(int i)
{
	if(i-dq[p]>=k)
		++p;
}

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