#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];
long long n, k;

deque<int>d;

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