#![allow(unused_imports)]
use std::cmp::*;

fn main() {
    let n = read::<usize>();
    let a = read_vec::<i64>();
    let mut ans = 0;
    for i in 0..n {
        for j in i + 1..n {
            ans = max(ans, a[i] ^ a[j]);
        }
    }
    println!("{}", ans);
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}