use std::cmp::max;

fn dfs(current: &mut Vec<usize>, used: &mut Vec<bool>, values: &Vec<usize>, n: usize) -> usize {
    let mut result: usize = 0;
    if current.len() == n / 2 {
        return current.iter().fold(0usize, |acc, &x| acc ^ x);
    }
    for i in 0..n {
        if used[i] { continue; }
        for j in i+1..n {
            if used[j] { continue; }
            used[i] = true;
            used[j] = true;
            current.push(values[i] + values[j]);
            result = max(result, dfs(current, used, values, n));
            current.pop();
            used[i] = false;
            used[j] = false;
        }
    }
    result
}

fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let n: usize = n.trim().parse().unwrap();
    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 current: Vec<usize> = vec![];
    let mut used: Vec<bool> = vec![false; n];
    println!("{}", dfs(&mut current, &mut used, &a, n));
}