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

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