#include<iostream>
#include<fstream>
#include<deque>
using namespace std;

struct Nod {
	int val, poz;
};

Nod make_nod(int val, int poz)
{
	Nod p;
	p.val = val;
	p.poz = poz;
	return p;
}

int main()
{
	ifstream fin("deque.in");
	ofstream fout("deque.out");
	deque<Nod> d;
	int n, k, current, i;
	long long rez = 0;
	fin >> n >> k;
	for(i = 0; i < k; i++)
	{
		fin >> current;
		while(!d.empty() && current <= d.back().val)
		{
			d.pop_back();
		}
		d.push_back(make_nod(current, i));
	}
	rez += d.front().val;
	for(i = k; i < n; i++)
	{
		fin >> current;
		while(!d.empty() && current <= d.back().val)
		{
			d.pop_back();
		}
		d.push_back(make_nod(current, i));
		while(d.front().poz <= i-k)
		{
			d.pop_front();
		}
		rez += d.front().val;
	}
	fout << rez;
	return 0;
}