/* -*- coding: utf-8 -*-
 *
 * 698.cc: No.698 ペアでチームを作ろう - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 14;
const int NBITS = 1 << MAX_N;

/* typedef */

/* global variables */

int as[MAX_N], dp[NBITS], bnums[NBITS];

/* subroutines */

inline void setmax(int &a, int b) { if (a < b) a = b; }

/* main */

int main() {
  int n;
  scanf("%d", &n);

  for (int i = 0; i < n; i++) scanf("%d", &as[i]);

  int nbits = 1 << n;

  bnums[0] = 0;
  for (int bits = 1, msb = 1; bits < nbits; bits++) {
    if ((msb << 1) <= bits) msb <<= 1;
    bnums[bits] = bnums[bits ^ msb] + 1;
  }
  
  for (int bits = 0, msb = 1; bits < nbits; bits++) {
    if (bnums[bits] & 1) continue;

    for (int i = 0, bi = 1; i < n; i++, bi <<= 1)
      if (! (bits & bi))
	for (int j = i + 1, bj = 1 << (i + 1); j < n; j++, bj <<= 1)
	  if (! (bits & bj))
	    setmax(dp[bits | bi | bj], dp[bits] + (as[i] ^ as[j]));
  }

  printf("%d\n", dp[nbits - 1]);
  return 0;
}