#include <fstream>
using namespace std;

ifstream in("deque.in");
ofstream out("deque.out");

const int N=5000005;
int v[N];
int dq[N],n,k,st,dr,i;
long long sum;

void dreapta (int i)
{
	while (st<=dr && v[dq[dr]]>=v[i])
		--dr;
}
void stanga(int i)
{
	if(i-dq[st]==k)
		++st;
}
void adauga (int i)
{
	dq[++dr]=i;
}

int main ()
{
	
	in>>n>>k;
	for(i=1;i<=n; ++i)
		in>>v[i];
	st=1;
	dr=0;
	sum=0;
	for(i=1; i<=k; i++)
	{
		dreapta(i);
		dq[++dr]=i;
	}
	sum+=v[dq[st]];
	for(;i<=n;i++)
	{
		stanga(i);
		dreapta(i);
		adauga(i);
		sum+=v[dq[st]];
	}
	
	out<<sum<<"\n";
	
	return 0;
}