#include <fstream>
#include <deque>
using namespace std;

int n, k;
deque< pair<int, int> > d;
long long s;

int main() {
	ifstream fin("deque.in");
	ofstream fout("deque.out");

	fin >> n >> k;
	for (int i = 0; i < n; ++i) {
		int v; fin >> v;
		
		while (!d.empty() && d.back().first > v)
			d.pop_back();
		d.push_back(make_pair(v, i));
		if (d.front().second + k == i)
			d.pop_front();

		s += i < k - 1 ? 0 : d.front().first;
	}
	fout << s;
}