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

using namespace std;

deque <int > deq;
vector <int> v1;
int n, k;

void citire()
{
	ifstream in("deque.in");
	in >> n >> k;

	int x;

	for (int i = 0; i < n; i++)
	{
		in >> x;
		v1.push_back(x);
	}

	in.close();



}

int main()
{
	int sum = 0;

	citire();


	for (int i = 0; i < n; i++)
	{
		while (!deq.empty() && v1[deq.back()] >= v1[i])
			deq.pop_back();

		deq.push_back(i);

		if (deq.front() == i - k)
			deq.pop_front();

		if (i >= k - 1)
			sum += v1[deq.front()];

	}


	ofstream out("deque.out");

	out << sum << endl;





	return 0;
}