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()).skip(1).collect();

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