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

using namespace std;

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

const int NMAX = 5000005;

int n, k;
long long sum = 0;

deque<int>d;
int v[NMAX];

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