func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long N = 2e5 + 2;   string s;   long long n;   long long func(vector<long long> a) {     stack<long long> st;     long long max_ = 0;     for (long long i = 0; i < n; i++) {       while (!st.empty() && a[i] > st.top()) {         long long cur = st.top();         st.pop();         max_ = max(cur ^ a[i], max_);       }       st.push(a[i]);     }     return max_;   }   void solve() {     cin >> n;     vector<long long> a(n);     for (long long i = 0; i < n; i++) {       cin >> a[i];     }     long long ans = func(a);     reverse(a.begin() + 0, a.end());     ans = max(ans, func(a));     cout << ans;   }   int32_t main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     cout.tie(NULL);     solve();     cout << endl;     return 0;   }   