fn main() {
    let n = {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.trim().parse::<usize>().unwrap()
    };
    let aa = {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        line.split_whitespace()
            .map(|x| x.parse::<usize>().unwrap())
            .collect::<Vec<_>>()
    };

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