#include <bits/stdc++.h>
using namespace std;
int a[100005];
int n;
int ml;
void work(int st, int nd) {
  if (nd - st + 1 < 2) {
    return;
  }
  int m = (st + nd) / 2;
  int sec;
  if (m > st) {
    sec = a[m - 1];
    for (int i = m - 1; i >= st; i--) {
      if (a[i] > sec) {
        sec = a[i];
      }
      if ((sec ^ a[m]) > ml) {
        ml = (sec ^ a[m]);
      }
      if (sec > a[m]) {
        break;
      }
    }
    work(st, m - 1);
  }
  if (m < nd) {
    sec = a[m + 1];
    for (int i = m + 1; i <= nd; i++) {
      if (a[i] > sec) {
        sec = a[i];
      }
      if ((sec ^ a[m]) > ml) {
        ml = (sec ^ a[m]);
      }
      if (sec > a[m]) {
        break;
      }
    }
    work(m + 1, nd);
  }
  int l, r;
  int la, ra;
  l = m - 1;
  r = m + 1;
  while (l >= st && a[l] < a[m]) {
    l--;
  }
  if (l >= st) {
    la = a[l];
  }
  while (r <= nd && a[r] < a[m]) {
    r++;
  }
  if (r <= nd) {
    ra = a[r];
  }
  while (l >= st && r <= nd) {
    if ((a[l] ^ a[r]) > ml) {
      ml = (a[l] ^ a[r]);
    }
    if (a[l] < a[r]) {
      while (l >= st && a[l] <= la) {
        l--;
      }
      if (l >= st) {
        la = a[l];
      }
    } else {
      while (r <= nd && a[r] <= ra) {
        r++;
      }
      if (r <= nd) {
        ra = a[r];
      }
    }
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
  }
  ml = -1;
  work(1, n);
  printf("%d\n", ml);
  return 0;
}
