#include <bits/stdc++.h>
using namespace std;
using ll = long long;
#define rep(i, s, e) for (int i = (int)s; i < (int)e; ++i)
#define all(a) (a).begin(), (a).end()

int main() {
    cin.tie(nullptr);
    
    int N;
    cin >> N;
    
    vector<ll> A(N);
    rep(i, 0, N) cin >> A[i];
    
    ll ans = -1;
    rep(i, 0, N - 1) rep(j, i + 1, N) ans = max(ans, A[i] ^ A[j]);
    
    cout << ans << '\n';
}