#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;

ll f(ll N){
	return ans;
}

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);
		rep(i,n){
			if((p.first>>i & 1)==0)continue;
			reg(j,i+1,n-1){
				if((p.first>>j & 1)==0)continue;
				ll q=p.first;
				q = q & ~(1<<i);
				q = q & ~(1<<j);
				Q.push(make_pair(q,p.second^(a[i]+a[j])));
			}
		}
	}
	cout<<ans<<endl;
}