#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <math.h>
#include <cmath>
#include<cctype>
#include<string>
#include<set>
#include<iomanip>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include<bitset>
#include <deque>
#include <climits>
#include <typeinfo>
#include <utility> 
using namespace std;
using ll = long long;
using R = double;
using Data = pair < ll, vector <ll>>;
const ll MOD = 1e9 + 7;
const ll inf = 1LL << 60;
struct edge { ll from; ll to; ll cost; };
typedef tuple<ll, ll, ll>T;
typedef pair<ll, ll>pll;
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(ll i = m;i < n;++i)
#define pb push_back
#define fore(i,a) for(auto &i:a)
#define rrep(i,m,n) for(ll i = m;i >= n;--i)
#define INF INT_MAX/2

int N,A[20],memo[1<<14];
int rec(int msk){
	if (memo[msk] != -1)return memo[msk];
	if (msk == 0)return 0;
	int ret = -1;
	rep(i, 0, N)rep(j, i+1, N) {
		if (((1<<i) & msk) && ((1<<j) & msk)) {
			memo[msk] = max(memo[msk], rec(msk-(1<<i)-(1<<j))+(A[i]^A[j]));
		}
	}
	return memo[msk];
}

int main(){
	cin >> N;
	rep(i, 0, N)cin >> A[i];
	memset(memo, -1, sizeof(memo));
	cout << rec((1<<N)-1) << endl;
	return 0;
}