#include <cstdio>

int dq[5000001],v[5000001],n,k,st=1,dr=0;
long long s;

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