#include <bits/stdc++.h>
using namespace std;
using ll = int_fast64_t;
const int mod = 1e9 + 7;
const int inf = (1 << 30) - 1;
const ll infll = (1LL << 61) - 1;
#define fast() ios::sync_with_stdio(false), cin.tie(nullptr)
#define digit(N) cout << fixed << setprecision((N))
#pragma GCC target("avx2")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")

int main()
{
	int N;
	cin >> N;
	vector<int> a(N);
	for (int i = 0; i < N; i++)
	{
		cin >> a[i];
	}

	vector<int> dp(1 << N);

	for (int bit = 0; bit < (1 << N); bit++)
	{
		int cnt = 0;

		for (int p = 0; p < N; p++)
		{
			if (bit & (1 << p))
				cnt++;
		}
		if (cnt % 2 == 1)
			continue;

		for (int j = 0; j < N; j++)
		{
			for (int k = 0; k < N; k++)
			{
				if (j == k)
					continue;
				if (bit & (1 << j))
					continue;
				if (bit & (1 << k))
					continue;

				dp[bit | (1 << j) | (1 << k)] = max(dp[bit | (1 << j) | (1 << k)], dp[bit] + (a[j] ^ a[k]));
			}
		}
	}

	cout << dp[(1 << N) - 1] << "\n";
}