#include<iostream>
#include<fstream>
#include<deque>
using namespace std;
int n,k,v[5000001],sum=0;
deque<int> deq;
void citire()
{
	ifstream fin("deque.in");
	fin>>n>>k;
	for (int i=0;i<n;i++)
		fin>>v[i];
	fin.close();
}
void minime()
{
	deq.resize(1);
	for (int i=0;i<n;i++)
	{
		while (!deq.empty() && v[i]<=v[deq.back()]) deq.pop_back();
		deq.push_back(i);
		if (deq.front()==i-k) deq.pop_front();
		if (i>=k-1) sum+=v[deq.front()];
	}
}		
int main ()
{
	citire();
	minime();
	ofstream fout("deque.out");
	fout<<sum;
	fout.close();
	return 0;
}