#include<cstdio>
#include<cstring>
#include<vector>
#include<queue>
#include<stack>
#include<algorithm>
#include<cmath>
#include<climits>
#include<string>
#include<set>
#include<numeric>
#include<map>
#include<iostream>
using namespace std;
#define rep(i,n) for(int i = 0;i<((int)(n));i++)
#define reg(i,a,b) for(int i = ((int)(a));i<=((int)(b));i++)
#define irep(i,n) for(int i = ((int)(n)-1);i>=0;i--)
#define ireg(i,a,b) for(int i = ((int)(b));i>=((int)(a));i--)
typedef long long ll;
typedef pair<ll, ll> mp;
ll mod = 1e9+7;
ll inf = 1e18;

//WA

ll n,A[100],ans=0;

int main(void){
	cin>>n;
	rep(i,n)cin>>A[i];
	queue<mp> Q;
	Q.push(make_pair((1<<n)-1,0));
	while(!Q.empty()){
		mp p = Q.front();Q.pop();
		if(p.first==0)ans=max(ans,p.second);
		vector<int> v;
		rep(i,n)if((p.first>>i & 1)==1)v.push_back(i);
		if(v.size()>=4){
			for(int a=0;a<v.size();a++){
				for(int b=a+1;b<v.size();b++){
					for(int c=a+1;c<v.size();c++){
						if(b==c)continue;
						for(int d=c+1;d<v.size();d++){
							if(b==d)continue;
							ll q=p.first;
							q = q & ~(1<<v[a]);
							q = q & ~(1<<v[b]);
							q = q & ~(1<<v[c]);
							q = q & ~(1<<v[d]);
							Q.push(make_pair(q,p.second^(A[v[a]]+A[v[b]])^(A[v[c]]+A[v[d]])));
						}
					}
				}
			}
		}else{//2
			rep(a,v.size()){
				reg(b,a+1,v.size()-1){
					ll q=p.first;
					q = q & ~(1<<v[a]);
					q = q & ~(1<<v[b]);
					Q.push(make_pair(q,p.second^(A[v[a]]+A[v[b]])));
				}
			}
		}
	}
	cout<<ans<<endl;
}

/*
14
387 137 192 123 29 193 753 210 821 437 1 1 1 1

*/