#include <bits/stdc++.h>

using ll = long long;

using namespace std;

int main()
{
    cin.tie(nullptr);
    ios::sync_with_stdio(false);

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

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

    int res{ 0 };
    for (int i =0; i < n-1; ++i)
    {
        for (int j = i+1; j < n; ++j)
            res = max(res, a[i]^a[j]);
    }

    printf("%d\n", res);

    return 0;
}