/* -*- coding: utf-8 -*-
 *
 * 1082.cc:  No.1082 XORのXOR - 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 = 2000;

/* typedef */

/* global variables */

int as[MAX_N];

/* subroutines */

/* main */

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

  int maxb = 0;
  for (int i = 0; i < n; i++)
    for (int j = i + 1; j < n; j++) {
      int b = as[i] ^ as[j];
      if (maxb < b) maxb = b;
    }

  printf("%d\n", maxb);
  return 0;
}