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