#include<iostream>
#include<cstdio>
#include<cstring>
#include <cstdlib>  
#include <cmath>   
#include<cctype>
#include<string>
#include<set>
#include <map>
#include<algorithm>
#include <functional>
#include<vector>
#include<climits>
#include<stack>
#include<queue>
#include <deque>
#include <typeinfo>
#include <utility> 
#define all(x) (x).begin(),(x).end()
#define rep(i,m,n) for(int i = m;i < n;++i)
using namespace std;
using ll = long long;
using R = double;
const ll inf = 1LL << 50;
const ll MOD = 1e9 + 7;


int n, A[14], dp[1 << 14];
void chmax(int &a,int b) {
	if (a == -1)a = b;
	else if (a < b)a = b;
}

int main() {
	cin >> n;
	rep(i, 0, n)cin >> A[i];
	memset(dp, -1, sizeof(dp));
	dp[0] = 0;
	rep(msk, 0, 1 << n)rep(a, 0, n - 1)rep(b, a + 1, n)if (!(msk&(1<<a)) && !(msk&(1<<b)) && dp[msk]>=0) {
		chmax(dp[msk+(1<<a)+(1<<b)],dp[msk]+(A[a]^A[b]));
	}

	cout << dp[(1<<n)-1] << endl;
	return 0;
}