import std.stdio, std.array, std.string, std.conv, std.algorithm;
import std.typecons, std.range, std.random, std.math, std.container;
import std.numeric, std.bigint, core.bitop, core.stdc.stdlib;

void main() {
    auto N = readln.chomp.to!int;
    auto A = readln.split.map!(to!long).array;

    long ans = 0;

    foreach (i; 0..N) foreach (j; i+1..N) {
        ans = max(ans, A[i] ^ A[j]);
    }

    ans.writeln;
}