#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);

    int n;
    cin >> n;

    vector<int> a(n);
    for (int i = 0; i < n; i++) {
        cin >> a[i];
    }

    int r = 0;
    for (int i = 0; i < n; i++) {
        for (int j = 0; j < i; j++) {
            r = max(r, a[i] ^ a[j]);
        }
    }

    cout << r << endl;

    return 0;
}