Vladik and Memorable Trip

题意翻译

一个区间 $\left[l,r\right]$ 合法当且仅当这个区间里的任何数不在区间外出现。一个区间的价值是其中所有出现的数的异或和，即重复的数只计算一次。将 $[1,n]$ 分成若干段合法区间，问它们的价值和最大是多少。

题目描述

Vladik often travels by trains. He remembered some of his trips especially well and I would like to tell you about one of these trips: Vladik is at initial train station, and now $ n $ people (including Vladik) want to get on the train. They are already lined up in some order, and for each of them the city code $ a_{i} $ is known (the code of the city in which they are going to). Train chief selects some number of disjoint segments of the original sequence of people (covering entire sequence by segments is not necessary). People who are in the same segment will be in the same train carriage. The segments are selected in such way that if at least one person travels to the city $ x $ , then all people who are going to city $ x $ should be in the same railway carriage. This means that they can’t belong to different segments. Note, that all people who travel to the city $ x $ , either go to it and in the same railway carriage, or do not go anywhere at all. Comfort of a train trip with people on segment from position $ l $ to position $ r $ is equal to XOR of all distinct codes of cities for people on the segment from position $ l $ to position $ r $ . XOR operation also known as exclusive OR. Total comfort of a train trip is equal to sum of comfort for each segment. Help Vladik to know maximal possible total comfort.

输入输出格式

输入格式

First line contains single integer $ n $ ( $ 1<=n<=5000 $ ) — number of people. Second line contains $ n $ space-separated integers $ a_{1},a_{2},...,a_{n} $ ( $ 0<=a_{i}<=5000 $ ), where $ a_{i} $ denotes code of the city to which $ i $ -th person is going.

输出格式

The output should contain a single integer — maximal possible total comfort.

输入输出样例

输入样例 #1

6
4 4 2 5 2 3

输出样例 #1

14

输入样例 #2

9
5 1 3 1 5 2 4 2 5

输出样例 #2

9

说明

In the first test case best partition into segments is: $ [4,4] $ $ [2,5,2] $ $ [3] $ , answer is calculated as follows: $ 4+(2 $ $ xor $ $ 5)+3=4+7+3=14 $ In the second test case best partition into segments is: $ 5 $ $ 1 $ $ [3] $ $ 1 $ $ 5 $ $ [2,4,2] $ $ 5 $ , answer calculated as follows: $ 3+(2 $ $ xor $ $ 4)=3+6=9 $ .