#include <iostream>

 #include <cstdio>

 #include <cstring>

 using namespace std;

 const int MAXN = ;

 int n, a[MAXN], l[MAXN], r[MAXN], vis[MAXN], dp[MAXN];

 int main()

 {

     cin >> n;

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

         cin >> a[i];

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

     {

         if (!l[a[i]]) l[a[i]] = i;

         r[a[i]] = i;

     }

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

     {

         dp[i] = dp[i - ];

         int cur = ;

         memset(vis, , sizeof(vis));

         int minL = l[a[i]];

         for (int j = i; j >= ; j--)

         {

             if (r[a[j]] > i) break;

             if (!vis[a[j]]) vis[a[j]] = , cur ^= a[j];

             minL = min(minL, l[a[j]]);

             if (minL >= j) dp[i] = max(dp[i], dp[j - ] + cur);

         }

     }

     cout << dp[n] << endl;

     return ;

 }