#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define P pair<ll,ll>
#define FOR(I,A,B) for(ll I = (A); I < (B); ++I)
#define FORR(I,A,B) for(ll I = ((B)-1); I >= (A); --I)
#define SORT(x) (sort(x.begin(),x.end())) // 0 2 2 3 4 5 8 9
#define REV(x) (reverse(x.begin(),x.end())) //reverse
ll gcd(ll a,ll b){if(a<b)swap(a,b);if(a%b==0)return b;else return gcd(b,a%b);}
ll lcm(ll a,ll b){ll c=gcd(a,b);return ((a/c)*(b/c)*c);}//saisyo kobaisu
#define NEXTP(x) next_permutation(x.begin(),x.end())
const ll INF=1e18+7;
const ll MOD=1e9+7;

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	ll n;
	cin >> n;
	vector<ll> a(n);
	FOR(i,0,n){
		cin >> a[i];
	}
	ll dp[1<<n];
	FOR(i,0,1<<n)dp[i]=0;
	FOR(S,0,1<<n){
		FOR(x,0,n){
			FOR(y,0,n){
				if(!(S&1<<x))if(!(S&1<<y)){
					dp[S|1<<x|1<<y] = max(dp[S|1<<x|1<<y],dp[S]+(a[x]^a[y]));
				}
			}
		}
	}
	cout << dp[(1<<n)-1] << endl;;
}