#include <cstdio>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <string>
#include <cstring>
using namespace std;
#define _ ios::sync_with_stdio(false)

const int MAXN = 5010;
const int INF = 0xfffffff;
typedef long long ll;

int n;
ll a[MAXN];
int l[MAXN], r[MAXN];
ll s[MAXN][MAXN];
int vis[MAXN];
ll dp[MAXN];
int main()
{
    scanf("%d", &n);
    for (int i = 1; i <= n; i++)
    {
        scanf("%I64d", a + i);
        if (l[a[i]])
            l[a[i]] = min(l[a[i]], i);
        else
            l[a[i]] = i;
        if (r[a[i]])
            r[a[i]] = max(r[a[i]], i);
        else
            r[a[i]] = i;
    }
    for (int i = 1; i <= n; i++)
    {
        memset(vis, 0, sizeof(vis));
        s[i][i] = a[i];
        vis[a[i]] = 1;
        for (int j = i + 1; j <= n; j++)
        {
            if (!vis[a[j]])
            {
                s[i][j] = s[i][j - 1] ^ a[j];
                vis[a[j]] = 1;
            }
            else
            {
                s[i][j] = s[i][j - 1];
            }
        }
    }
    dp[0] = 0;
    for (int i = 1; i <= n; i++)
    {
        int temp = a[i];
        if (i == r[temp])
        {
            int L = l[temp];
            int ok = 1;
            for (int j = l[temp] + 1; j < r[temp]; j++)
            {
                if (r[a[j]] > i)
                {
                    ok = 0;
                    break;
                }
                L = min(l[a[j]], L);
            }
            if (ok)
                dp[i] = max(dp[i - 1], dp[L - 1] + s[L][i]);
            else
                dp[i] = dp[i - 1];
        }
        else
            dp[i] = dp[i - 1];
    }
    printf("%I64d\n", dp[n]);
}