#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

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

    int ret = 0;
    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            ret = max(ret, a[i] ^ a[j]);
        }
    }

    cout << ret << endl;
    return 0;
}