fn main() {
    let n: usize = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        buf.trim_end().parse().unwrap()
    };

    let a: Vec<usize> = {
        let mut buf = String::new();
        std::io::stdin().read_line(&mut buf).unwrap();
        let iter = buf.split_whitespace();
        iter.map(|x| x.parse().unwrap()).collect()
    };

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