I have a wrong answer on test case 12, but I have no idea what is wrong. Here is my code:

import java.util.Arrays; import java.util.Scanner;

public class D2416C {

public static void main(String[] args) {

    Scanner s = new Scanner(System.in);
    int n = s.nextInt();
    s.nextLine();
    String lin = s.nextLine();
    int[] arr = new int[n];
    int[] st = new int[5001];
    int[] nd = new int[5001];
    String[] linarr = lin.split(" ");
    Arrays.fill(st, -1);
    Arrays.fill(nd, -2);
    for(int i = 0; i < n; i++){
       arr[i] = Integer.parseInt(linarr[i]);
       if(st[arr[i]]==-1)
         st[arr[i]] = i;
    }
    for(int j = n-1;j >= 0; j--)
       if(nd[arr[j]]==-2)
         nd[arr[j]]=j;
    for(int i = 1; i < arr.length; i++)
       arr[i]= arr[i]^arr[i-1];

    int[] max = new int[n];

    max[0] = 0;
    for(int i = 0; i < nd.length; i++) 
       if(nd[i] == 0)
         max[0] = i;

    for(int i = 1; i < n; i++){
       int k = 0;
       for(int j = 0; j < nd.length; j++){
         if(nd[j]==i){
          k = j;
          break;
         }       
       }
       if(k != 0){
         if(st[k] == 0)
          max[i] = Math.max(max[i-1],arr[st[k]]);
         else
          if(st[k] == nd[k])
              max[i] = max[i-1]+k;
         else{
           if(st[k]== 1)
            max[i] = Math.max(max[i-1],(arr[nd[k]-1]^arr[st[k]-1]));
           else{
            int qw = arr[nd[k]-1]^arr[st[k]-1];
            max[i] = Math.max(max[i-1],qw+max[st[k]-2]);
           }
         }
       }
       else
         max[i] = max[i-1];
    }

    System.out.println(max[n-1]);

}

}