#include <iostream>
#include <fstream>
#include <queue>

using namespace std;

ifstream f ("deque.in");
ofstream g ("deque.out");


const int NMAX = 5000000;

int n, k;
int v[NMAX + 1];

void rezolva() {
	f >> n >> k;
	deque <int> dq;

	long long sol = 0;

	for (int i = 1; i <= n; i++) {
		f >> v[i];

		while (!dq.empty() && v[dq.back()] > v[i])
			dq.pop_back();
		dq.push_back(i);

		if (dq.front() == i - k) dq.pop_front();
		if (i >= k) sol += v[dq.front()];
	}

	g << sol << '\n';
}

int main() {
	rezolva();
	return 0;
}