use std::{collections::BinaryHeap, cmp::Reverse};


fn main() {
    let mut nk = String::new();
    std::io::stdin().read_line(&mut nk).ok();
    let nk: Vec<usize> = nk.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();
    let n = nk[0];
    let k = nk[1];
    let mut a = String::new();
    std::io::stdin().read_line(&mut a).ok();
    let a: Vec<usize> = a.trim().split_whitespace().map(|s| s.parse().unwrap()).collect();

    let mut summary = 0usize;
    let mut result = 0usize;
    let mut pque = BinaryHeap::new();
    for i in (1..n).rev() {
        if pque.len() < k {
            summary += a[i];
            pque.push(Reverse(a[i]));
            if i % 2 == 1 {
                result = summary;
            }
        } else {
            if i % 2 == 1 {
                result = result.max(summary - pque.peek().unwrap().0 + a[i]);
            }
            pque.push(Reverse(a[i]));
            summary += a[i];
            summary -= pque.pop().unwrap().0;
        }
    }
    println!("{}", result);
}