#include <fstream>
#include <deque>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
const int NMAX = 5000005;
int a[NMAX];
deque<int> D;
int main()
{
	int n, k;
	f >> n >> k;
	long long s = 0;
	for (int i = 1; i <= n; i++)
		f >> a[i];
	for (int i = 1; i <= n; i++)
	{
		while (!D.empty() && a[i] <= a[D.back()])
			D.pop_back();
		D.push_back(i);
		while (D.front() <= i - k)
			D.pop_front();
		if (i >= k)
			s += a[D.front()];
	}
	g << s << "\n";
	return 0;
}