use std::{collections::BTreeMap, 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 mut 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 stock = BTreeMap::new();
    let mut a = a.into_iter().skip(1).enumerate().collect::<Vec<(usize, usize)>>();
    a.sort_by_key(|&(i, v)| (Reverse(v), i % 2, i));
    a.reverse();
    let mut result = 0usize;
    let mut minidx = n;
    while k > 0 {
        let (idx, val) = a.pop().unwrap();
        if idx % 2 == 0 {
            minidx = idx.min(minidx);
            result += val;
            k -= 1;
            let mut targets = stock.range(idx..).map(|(&idx, &v)| (idx, v)).collect::<Vec<(usize, usize)>>();
            targets.sort_by_key(|&(_, v)| Reverse(v));
            let limit = k.min(targets.len());
            for i in 0..limit {
                let (idx, v) = targets[i];
                stock.remove(&idx);
                result += v;
                k -= 1;
            }
        } else if idx > minidx {
            k -= 1;
            result += val;
        } else {
            stock.insert(idx, val);
        }
    }
    println!("{}", result);
}