import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int k = sc.nextInt();
        int[] values = new int[n];
        for (int i = 0; i < n; i++) {
            values[i] = sc.nextInt();
        }
        long sum = 0;
        PriorityQueue<Integer> queue = new PriorityQueue<>();
        for (int i = 0; i < k - 1; i++) {
            sum += values[n - i - 1];
            queue.add(values[n - i - 1]);
        }
        long ans = 0;
        for (int i = n - k; i >= 0; i--) {
            if (i % 2 == 1) {
                while (queue.size() > k - 1) {
                    sum -= queue.poll();
                }
                ans = Math.max(ans, sum + values[i]);
            }
            queue.add(values[i]);
            sum += values[i];
        }
        System.out.println(ans);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}