use std::cmp::*;
use std::io::*;

fn main() {
    let mut s: String = String::new();
    std::io::stdin().read_to_string(&mut s).ok();
    let mut itr = s.trim().split_whitespace();
    let n: usize = itr.next().unwrap().parse().unwrap();
    let a: Vec<usize> = (0..n)
        .map(|_| itr.next().unwrap().parse().unwrap())
        .collect();

    let mut ans = 0;
    for i in 0..n {
        for j in i + 1..n {
            ans = max(ans, a[i] ^ a[j]);
        }
    }

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