#include<bits/stdc++.h>
using namespace std;
 
long long arr[5001];
 
vector< vector<long long int> > v;
 
 
long long dp[5010],a[5010];
long long N;
int mx[5010],maxx[5010];
long long recurse(int x){
if(x>=N)
return 0;
long long ans=0;
 
if(dp[x]!=-1)
return dp[x];
long long val=0;
for(int i=x;i<N;i++){
if(mx[a[i]]>=x && maxx[a[i]]==i ){
    val^=a[i];
}
ans=max(ans,val+recurse(i+1));
 
}
return dp[x]=ans;
}
 
int main(){
cin>>N;
int i,j;
for(i=0;i<5001;i++){
    mx[i]=INT_MAX;
}
for(i=0;i<N;i++){
scanf("%lld",&a[i]);
mx[a[i]]=min(i,mx[a[i]]);
maxx[a[i]]=max(i,maxx[a[i]]);
dp[i]=-1;
}
 
cout<<recurse(0)<<endl;;
return 0;
}

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