import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.PriorityQueue;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		int n = Integer.parseInt(sa[0]);
		int k = Integer.parseInt(sa[1]);
		sa = br.readLine().split(" ");
		int[] a = new int[n + 1];
		for (int i = 0; i < n; i++) {
			a[i] = Integer.parseInt(sa[i]);
		}
		br.close();

		PriorityQueue<Integer> que = new PriorityQueue<>();
		long val = 0;
		long ans = 0;
		for (int i = n / 2 * 2 - 1; i > 0; i -= 2) {
			val += a[i];
			if (i < n - 1) {
				que.add(a[i + 1]);
				val += a[i + 1];
			}
			if (que.size() > k - 1) {
				int x = que.poll();
				val -= x;
			}
			ans = Math.max(ans, val);
			que.add(a[i]);
			if (que.size() > k - 1) {
				int x = que.poll();
				val -= x;
			}
		}
		System.out.println(ans);
	}
}