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

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

deque <int> deq;

int arr[5000001];

int main() {
	int n, k;
	f >> n >> k;
	for (int i = 1; i <= n; i++) {
		f >> arr[i];
	}
	long long sum = 0, back;
	for (int i = 1; i <= n; i++) {
		back = deq.size() - 1;
		while(back >= 0 && arr[i] <= arr[deq.back()]) {
			deq.pop_back();
			back--;
		}
		deq.push_back(i);
		if (deq.front() == i - k) {
			deq.pop_front();
		}
		if (i >= k) {
			sum += arr[deq.front()];
		}
	}
	g << sum << "\n";
	return 0;
}