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

#define maxLn 50000010

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

deque <long long> deq;

long long arr[maxLn];

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