#include <bits/stdc++.h>
int diru[] = {-1, -1, -1, 0, 0, 1, 1, 1};
int dirv[] = {-1, 0, 1, -1, 1, -1, 0, 1};
using namespace std;
struct debugger {
  template <typename T>
  debugger& operator,(const T& v) {
    cerr << v << " ";
    return *this;
  }
} dbg;
template <class T>
T sq(T n) {
  return n * n;
}
template <class T>
T gcd(T a, T b) {
  return (b != 0 ? gcd<T>(b, a % b) : a);
}
template <class T>
T lcm(T a, T b) {
  return (a / gcd<T>(a, b) * b);
}
template <class T>
bool inside(T a, T b, T c) {
  return a <= b && b <= c;
}
template <class T>
void setmax(T& a, T b) {
  if (a < b) a = b;
}
template <class T>
void setmin(T& a, T b) {
  if (b < a) a = b;
}
template <class T>
T power(T N, T P) {
  return (P == 0) ? 1 : N * power(N, P - 1);
}
int n;
int in[100010];
int q[100010];
int solve() {
  int len = 0, i, ret = 0;
  for (i = 0; i < n; i++) {
    while (len && in[i] > q[len - 1]) {
      ret = max(ret, in[i] ^ q[len - 1]);
      len--;
    }
    q[len++] = in[i];
  }
  return ret;
}
int main() {
  int T, t = 1, m, i, j, k;
  scanf("%d", &n);
  for (i = 0; i < n; i++) scanf("%d", &in[i]);
  m = solve();
  reverse(in, in + n);
  m = max(m, solve());
  printf("%d\n", m);
  return 0;
}
