#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;
using vi = vector<int>;

int main()
{
    int N;
    cin >> N;
    vi A(N);
    for (int i = 0; i < N; ++i)
        cin >> A[i];
    
    int ans = -1;
    for (int i = 0; i < N; ++i)
    {
        for (int j = i + 1; j < N; ++j)
        {
            ans = max(ans, A[i] ^ A[j]);
        }
    }
    cout << ans << endl;
}