#include <bits/stdc++.h>   using namespace std;   template <class T>   inline T gcd(T a, T b) {     return b ? gcd(b, a % b) : a;   }   template <class T>   inline T LCM(T a, T b) {     if (a < 0) return LCM(-a, b);     if (b < 0) return LCM(a, -b);     return a * (b / gcd(a, b));   }   vector<int> arr;   const int N = 50005;   int memo[5001];   int save[N];   int visit[N];   int find(int pos, int &xr) {     for (int i = 0; i < N; i++) visit[i] = 0;     vector<int> toAdd;     int end = pos;     visit[arr[pos]] = 1;     for (int i = 0; i < pos; i++) {       visit[arr[i]] = 2;     }     if (visit[arr[pos]] == 2) {       return -1;     }     bool cant = false;     for (int i = pos; i < arr.size(); i++) {       if (visit[arr[i]] == 2) {         cant = true;       }       if (visit[arr[i]] == 1) {         if (cant) return -1;         for (int j = 0; j < toAdd.size(); j++) {           visit[toAdd[j]] = 1;         }         toAdd.clear();         end = i;       } else {         toAdd.push_back(arr[i]);       }     }     xr = 0;     for (int i = 0; i < N; i++) {       if (visit[i] == 1) {         xr = xr ^ i;       }     }     return end;   }   int solve(int from) {     int txr = 0;     int ret = 0;     if (from >= arr.size()) return 0;     if (memo[from] != -1) {       return memo[from];     }     int end = find(from, txr);     if (end != -1) {       ret = max(txr + solve(end + 1), solve(from + 1));     } else {       ret = solve(from + 1);     }     memo[from] = ret;     return ret;   }   int main() {     int n, i, temp, j;     for (i = (int)0; i < (int)5001; ++i) {       memo[i] = -1;     }     scanf( %d , &n);     for (i = (int)0; i < (int)n; ++i) {       scanf( %d , &temp);       arr.push_back(temp);     }     int xx;     cout << solve(0);     return 0;   }   