#include <iostream>
#include <vector>
using namespace std;
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, 0);
	for (int i = 0; i < (1 << N); i++){
		for (int j = 0; j < N; j++){
			for (int k = j + 1; k < N; k++){
				if ((i >> j & 1) && (i >> k & 1)){
					dp[i] = max(dp[i], dp[i - (1 << j) - (1 << k)] + (A[j] ^ A[k]));
				}
			}
		}
	}
	cout << dp[(1 << N) - 1] << endl;
}