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 mut a: Vec<usize> = a.trim().split_whitespace().skip(1).map(|s| s.parse().unwrap()).collect();

    let mut result = 0usize;
    let mut pque = BinaryHeap::new();
    let mut summary = 0usize;
    for _ in 0..k {
        let val = a.pop().unwrap();
        summary += val;
        pque.push(Reverse(val));
    }
    if a.len() % 2 == 0 {
        result = summary;
    }
    while a.len() > 0 {
        let val = a.pop().unwrap();
        if a.len() % 2 == 0 {
            result = result.max(summary + val - pque.peek().unwrap().0);
        }
        summary += val;
        pque.push(Reverse(val));
        summary -= pque.pop().unwrap().0;
    }
    println!("{}", result);
}