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

using namespace std;

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

std::deque<long long> D;
int Arr[5000001];
long long S = 0;

int main()
{
	int n, k;
	fin >> n >> k;

	for (int i = 1; i <= n; i++) {
		fin >> Arr[i];
	}

	for (int i = 1; i <= n; i++)
	{
		while (!D.empty() && Arr[i] <= Arr[D.back()]) {
			D.pop_back();
		}
		D.push_back(i);

		if (!D.empty() && D.front() == i - k) {
			D.pop_front();
		}

		if (!D.empty() && i >= k) {
			S += Arr[D.front()];
		}
	}

	fout << S;

	return 0;
}