Bike loves looking for the second maximum element in the sequence. The second maximum element in the sequence of distinct numbers x 1, x 2, …, x k (k > 1) is such maximum element x j, that the following inequality holds: 
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The lucky number of the sequence of distinct positive integers x 1, x 2, …, x k (k > 1) is the number that is equal to the bitwise excluding OR of the maximum element of the sequence and the second maximum element of the sequence.
You’ve got a sequence of distinct positive integers s 1, s 2, …, s n (n > 1). Let’s denote sequence s l, s l + 1, …, s r as s[l..r] (1 ≤ l < r ≤ n). Your task is to find the maximum number among all lucky numbers of sequences s[l..r].
Note that as all numbers in sequence s are distinct, all the given definitions make sence.
Input
The first line contains integer n (1 < n ≤ 105). The second line contains n distinct integers s 1, s 2, …, s n (1 ≤ s i ≤ 109).
Output
Print a single integer — the maximum lucky number among all lucky numbers of sequences s[l..r].
Examples
input
5
5 2 1 4 3
output
7
input
5
9 8 3 5 7
output
15
Note
For the first sample you can choose s[4..5] = {4, 3} and its lucky number is (4 xor 3) = 7. You can also choose s[1..2].
For the second sample you must choose s[2..5] = {8, 3, 5, 7}.
Solution:
#include <iostream>
#include <iomanip>
#include <stdio.h>
#include <set>
#include <vector>
#include <map>
#include <cmath>
#include <algorithm>
#include <memory.h>
#include <string>
#include <sstream>
using namespace std;
int a[111111];
int main() {
int n;
scanf("%d", &n);
int e = 0, ans = 0;
for (int i=0;i<n;i++) {
int x;
scanf("%d", &x);
while (e > 0) {
if ((x ^ a[e]) > ans) ans = (x ^ a[e]);
if (x > a[e]) e--;
else break;
}
a[++e] = x;
}
printf("%d\n", ans);
return 0;
}
