#include <cmath>

#include <stack>

#include <cstdio>

#include <vector>

#include <iostream>

#include <algorithm>

using namespace std;

int main() {

    int n; cin >> n;

    vector<int> in(n);

    for(int i = ; i < n; i ++)

        cin >> in[i];

    int ret = ;

    {

        in.push_back();

        stack<int> stk;

        for (int i = ; i < in.size(); i++)

        {

            if (stk.empty() || in[i] > stk.top())

            {

                stk.push(in[i]);

            }

            else

            {

                int lastV = stk.top(); stk.pop();

                if (!stk.empty())

                {

                    ret = std::max(ret, (lastV ^ stk.top()));

                    //cout << lastV << "-" << stk.top() << "=" << (lastV ^ stk.top()) << endl;

                }

                i--;

            }

        }

        in.pop_back();

    }

    {

        stack<int> stk;

        in.insert(in.begin(), );

        for (int i = in.size() - ; i >= ; i --)

        {

            if (stk.empty() || in[i] > stk.top())

            {

                stk.push(in[i]);

            }

            else

            {

                int lastV = stk.top(); stk.pop();

                if (!stk.empty())

                {

                    ret = std::max(ret, (lastV ^ stk.top()));

                    //cout << lastV << "-" << stk.top() << "=" << (lastV ^ stk.top()) << endl;

                }

                i++;

            }

        }

    }

    cout << ret << endl;

    return ;

}