#include <iostream>
#include <fstream>
#include <cmath>
#include <vector>
#include <queue>
#include <deque>
#include <list>
#include <string>
#include <algorithm>
using namespace std;
ifstream ff("deque.in");
ofstream gg("deque.out");

int n, k;
long long s;
struct tuplu{ int x,y; tuplu(int x0=0,int y0=0){x=x0;y=y0;} };
deque<tuplu> dd;

int main(){
	int x;
	ff >> n >> k;
	for(int i=0;i<k;i++){
		ff >> x;
		while(dd.size()>0 && dd.back().x>=x)dd.pop_back();
		dd.push_back(tuplu(x,i));
	}
	s=dd.front().x;
	for(int i=k;i<n;i++){
		ff >> x;
		while(dd.size()>0 && dd.front().y<=i-k)dd.pop_front();
		while(dd.size()>0 && dd.back().x>=x)dd.pop_back();
		dd.push_back(tuplu(x,i));
		s+=dd.front().x;
	}
	gg << s;
	return 0;
}