#include <fstream>
#include <deque>

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

int n, k;
long long int sum;

struct element
{
	int nr, poz;
} x;

deque <element> dq;

int main()
{
	int i, j;

	fin >> n >> k;

	fin >> x.nr; x.poz = 1;

	dq.push_front(x);

	for (i = 2; i < k; ++i)
	{
		fin >> x.nr; x.poz = i;
		while (!dq.empty() && x.nr < dq.back().nr)
			dq.pop_back();

		dq.push_back(x);
	}

	for (i = k; i <= n; ++i) 
	{
		fin >> x.nr; x.poz = i;

		if (dq.front().poz == i - k)
		{
			dq.pop_front();
		}

		while (!dq.empty() && x.nr < dq.back().nr)
			dq.pop_back();

		dq.push_back(x);

		sum += dq.front().nr;
	}

	fout << sum << '\n';


	return 0;
}