#include <bits/stdc++.h>
using namespace std;
using lint     = long long;
const lint inf = 1LL << 60;
const lint mod = 1000000007;

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    lint n;
    cin >> n;
    vector<lint> a(n);
    for (int i = 0; i < n; ++i) {
        cin >> a[i];
    }
    lint 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 << "\n";
    return 0;
}