#include <bits/stdc++.h>
#define SF(x) scanf("%I64d",&x)
#define F first
#define S second
#define MEM(a,b) memset(a,b,sizeof(a))
#define DB(x) cout << #x << " is " << x << endl
#define ffs(x) __builtin_ffs(x) // This function returns 1 + least significant 1-bit of x. If x == 0, returns 0. Here x is int, this function with suffix 'l' gets a long argument and with suffix 'll' gets a long long argument.
#define clz(x) __builtin_clz(x) // This function returns number of leading 0-bits of x which starts from most significant bit position. x is unsigned int and like previous function this function with suffix 'l gets a unsigned long argument and with suffix 'll' gets a unsigned long long argument. If x == 0, returns an undefined value.
#define ctz(x) __builtin_ctz(x) // This function returns number of trailing 0-bits of x which starts from least significant bit position. x is unsigned int and like previous function this function with suffix 'l' gets a unsigned long argument and with suffix 'll' gets a unsigned long long argument. If x == 0, returns an undefined value.
#define popcount(x) __builtin_popcount(x) // This function returns number of active bits in the binary represintation of the number
#define pb push_back

using namespace std;
typedef long long ll;

ll Mypow(ll X,ll Y){
    if(Y < 0)return 0;
    if(Y == 0)return 1;
    if(Y == 1){
        return X;
    }
    else{
        ll x = Mypow(X ,Y / 2);
        x *= x;
        if(Y % 2)
            return (x * X);
        else
            return x;
    }
}

int dp[5010][5010];
int n, a[5010];
pair < int, pair < int , int > > arr1[5010];
int endd[5010];
int start[5010];
int k = 1;
bool vis[5010];
bool B[5010];

int DP(int pos1, int pos2)
{
    if(pos1 > k)
        return 0;
    int &cur = dp[pos1][pos2];
    if(cur != -1){
        return cur;
    }
    cur = DP(pos1 + 1, pos2);
    if(arr1[pos1].F > pos2){
        cur = max(cur, DP(pos1 + 1, arr1[pos1].S.F) + arr1[pos1].S.S);
    }
    return cur;
}

int main()
{
    cin >> n;
    for(int i = 1 ; i <= n ; i++){
        cin >> a[i];
    }
    for(int i = n ; i > 0 ; i--){
        if(!vis[a[i]]){
            vis[a[i]] = true;
            endd[a[i]] = i;
        }
    }
    memset(vis, 0, sizeof(vis));
    for(int i = 1 ; i <= n ; i++){
        if(!vis[a[i]]){
            vis[a[i]] = true;
            start[a[i]] = i;
        }
    }
    memset(vis, 0, sizeof(vis));
    for(int i = 1 ; i <= n ; i++){
        if(start[a[i]] == i){
            int des = endd[a[i]];
            int j;
            for(j = i ; j <= des ; j++){
                des = max(des, endd[a[j]]);
            }
            j--;
            arr1[k].F = i;
            arr1[k].S.F = j;
            memset(B, 0, sizeof(B));
            for(int l = i ; l <= j ; l++){
                if(!B[a[l]]){
                    B[a[l]] = true;
                    arr1[k].S.S ^= a[l];
                }
            }
            k++;
        }
    }
    k--;
    sort(arr1 + 1, arr1 + k);
    memset(dp, -1, sizeof(dp));
    cout << DP(1, 0) << endl;
    return 0;
}