#include <fstream>
#include <deque>

using namespace std;

const int NMAX = 5000005;
int n, k, v[NMAX];
deque <int> dq;

int main()
{
	ifstream fin("deque.in");
	ofstream fout("deque.out");
	fin >> n >> k;
	for (int i = 1;i <= n;++i)
		fin >> v[i];
	long long s = 0;
	for (int i = 1;i <= n;++i)
	{
		while (!dq.empty() && v[i] <= v[dq.back()])
			dq.pop_back();
		dq.push_back(i);
		if (i - k == dq.front())
			dq.pop_front();
		if (i >= k)
			s += v[dq.front()];
	}
	fout << s << "\n";
	fin.close();
	fout.close();
	return 0;
}