use proconio::input;
use std::io::{stdout,Write,BufWriter};

fn main() {
    input!{
        n:usize,
        a:[usize;n]
    }

    let out = stdout();
    let mut out = BufWriter::new(out.lock());
    
    let mut max = 0;
    for i in 0..a.len() {
        for j in i+1..a.len() {
            max = max.max(a[i]^a[j]);
        }
    }
    write!(out, "{}", max).unwrap();
}