#![allow(non_snake_case)]
#[allow(unused_imports)]
use proconio::{fastout, input, marker::*};

#[fastout]
fn main() {
    input! {
        N: usize,
        A: [isize; N],
    }

    let mut ans = 0;
    let mut S = A.iter().cloned().collect::<std::collections::BTreeSet<_>>();

    for i in 0..N {
        if i % 2 == 0 {
            let m = S.pop_last().unwrap();
            ans += m;
        } else {
            let m = S.pop_last().unwrap();
            ans += -(-m);
        }
    }

    println!("{}", ans);
}