#include <bits/stdc++.h>

using namespace std;

using ll = long long;
using ld = long double;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using vi = vector<int>;

#define pb push_back
#define eb emplace_back
#define fi first
#define se second
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
#define rep(i,a,b) for (int i = (a); i < (b); ++i)

mt19937 rng(random_device {}());

int main()
{
    cin.tie(0)->sync_with_stdio(0);

    int n;
    cin >> n;
    vi a(n);
    rep(i,0,n) cin >> a[i];

    int ans = 0;
    rep(i,0,n){
        rep(j,i+1,n){
            ans = max(ans, a[i]^a[j]);
        }
    }

    cout << ans << endl;

    return 0;
}