#include<iostream>
#include<climits>
#include<set>
#include<map>
#include<vector>
#include<string>
#include<algorithm>
#include<math.h>
#include<queue>
#include<deque>
#include<stack>
#include<assert.h>
#include<numeric>
#include<bitset>

#define rep(i,a,b) for(int i=a;i<b;i++)
#define rrep(i,a,b) for(int i=a;i>=b;i--)
#define fore(i,a) for(auto &i:a)
#define all(x) (x).begin(),(x).end()

typedef long long ll;
using namespace std;
const int inf = INT_MAX / 2;
const ll infl = 1LL << 62;
const double PI = 2 * acos(0.0);
template<class T>bool chmax(T& a, const T& b) { if (a < b) { a = b; return 1; } return 0; }
template<class T>bool chmin(T& a, const T& b) { if (b < a) { a = b; return 1; } return 0; }
ll gcd(ll a, ll b) { return a ? gcd(b % a, a) : b; }

int n;
int A[20];
int dp[20000];
int main() {
	cin >> n;
	for (int i = 0; i < n; i++) cin >> A[i];

	for (int msk = 0; msk < 1 << n; msk++) {
		for (int a = 0; a < n; a++) for (int b = a + 1; b < n; b++) {
			if (!(msk & 1 << a) && !(msk & 1 << b)) {
				chmax(dp[msk + (1 << a) + (1 << b)], dp[msk] + (A[a] ^ A[b]));
			}
		}
	}

	cout << dp[(1 << n) - 1] << endl;
}