#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < n; i++)
using namespace std;

typedef long long ll;

int main() {
    int N, ans = 0;
    cin >> N;
    vector<int> A(N);
    rep(i, N) cin >> A[i];
    rep(i, N) {
        rep(j, N) {
            ans = max(ans, A[i] ^ A[j]);
        }
    }
    cout << ans << "\n";
}