#include<stdio.h>
int dq[1<<23],v[1<<23];
int n,k,i,st=1,dr=0;
long long s;
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()
{
	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);
	for(i=k;i<=n;++i)
	{
		stanga(i);
		dreapta(i);
		s+=v[dq[st]];
	}
	printf("%lld",s);
	return 0;
}