fn main() {
    let mut xx = String::new();
    std::io::Read::read_to_string(&mut std::io::stdin(), &mut xx).ok();
    let xx: Vec<u64> = xx.split_whitespace().skip(1).flat_map(str::parse).collect();

    let mut max = 0;
    for i in 0..xx.len() {
        for j in 0..i {
            max = max.max(xx[i] ^ xx[j]);
        }
    }

    println!("{max}");
}