#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
int n;
vector <int> a(5001,0);
vector < vector <int> > x(5001,vector <int>(5001,0));
vector <int> dp(5001,0);
vector <int> first(5001,10e6);
vector <int> last(5001,0);




int cur(int left, int right)
{

    int pff(0);

    for (int i=left;i<=right;i++)
    {
        for (int j=i;j<=right;j++)
        {

            if (a[i]!=a[j])
            {


                pff=max(pff,x[i][j]);
                //cout << x[i][j] << " ";
            }
            else{
                pff=max(pff,a[i]);
               // cout << i << " ";
            }
            //cout << a[i] << " ";
        }
    }
    return pff;

}

int main()
{
        ios::sync_with_stdio(0); cin.tie(0) ; cout.tie(0);

        #ifdef _DEBUG
        cout << setprecision(6)  << fixed ;
        #endif



        for (int i=1;i<=5000;i++)
       {
           for (int j=i+1;j<=5000;j++)
           {
               ll pf=i^j;
               x[i][j]=pf;
               x[j][i]=pf;
           }
       }
        cin >> n;
       for (int i=1;i<=n;i++)
       {
           cin >> a[i];
           first[a[i]]=min(first[a[i]],i);
           last[a[i]]=max(last[a[i]],i);

       }


       //cout << cur (1 , 2);



       for (int i=1;i<=n;i++)
       {
           for (int j=i;j>=1;j--)
           {

                    bool cheker=true;
                    for (int z=j;z<=i and cheker==true;z++)
                    {
                        if (first[a[z]]>=j and last[a[z]]<=i)
                        {

                        }
                        else{
                            cheker=false;
                        }
                        //cout << cheker << " " << i << " ";

;                    }
                    if (cheker)
                    {
                        dp[i]=max(dp[i],dp[j-1]+cur(i , j));
                        //cout << cur(i , j) << "\n";

                    }
                    else{
                        dp[i]=max(dp[i],dp[i-1]);
                    }

                    if (i==j and first[a[i]]==i and last[a[i]]==i)
                    {
                        dp[i]=max(dp[i] , a[i]);
                    }

                    //cout << cur(i , j) << "\n" ;



           }

       }






//cout << dp[n] << " ";
/*for (int i=1;i<=n;i++)
{
    cout << first[i] <<" "  <<last[i] << "\n";
}
*/
        return 0;

}