/*
 * deque.cpp
 *
 *  Created on: Feb 15, 2013
 *      Author: Heghedus Razvan
 */
#include<iostream>
#include<deque>
#include<fstream>
#define DIM 5000001
using namespace std;

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

deque<int> deck;
int n,k,v[DIM];
long long s;
int main()
{
	f>>n>>k;
	for(int i=1;i<=n;i++)
	{
		f>>v[i];
		while(!deck.empty() && deck.back()>v[i])	deck.pop_back();
		deck.push_back(v[i]);
		if(i>k && deck.front()==v[i-k])	deck.pop_front();
		if(i>=k) s+=deck.front();
	}
	g<<s;
	return 0;
}