#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
ld pie=3.141592653589793;
ll inf=10010010010010010;
ll mod=998244353;
int main(){
    ll n;
    cin >> n;
    vector<ll>a(n);
    for (ll i = 0; i < n; i++)
    {
        cin >> a[i];
    }
    ll ans=0;
    for (ll i = 0; i < n; i++)
    {
        for (ll j = i+1; j < n; j++)
        {
            ans=max(ans,a[i]^a[j]);
        }
    }
    cout << ans << endl;
}