#include <iostream>
#include <fstream>
#include <deque>
#include <algorithm>
#include <map>

using namespace std;

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

const int NMAX = 5000005;
int v[NMAX];
int n, k;

deque<int>d;

int main()
{
	fin >> n >> k;
	long long sum = 0;
	for (int i = 1; i <= k; i++)
	{
		fin >> v[i];
		if (d.empty())
		{
			d.push_back(i);
			continue;
		}
		while (!d.empty() && v[i] <= v[d.front()])
			d.pop_front();
		d.push_back(i);
	}
	sum += (1ll * v[d.front()]);
	for (int i = k + 1 ; i <= n ; i++)
	{
		fin >> v[i];
		if (d.empty())
		{
			d.push_back(i);
			continue;
		}
		while (!d.empty() && (v[i] <= v[d.front()] || i-d.front()+1 > k) )
			d.pop_front();
		d.push_back(i);
		sum += (1ll * v[d.front()]);
	}
	fout << sum << "\n";
	return 0;
}