func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename T1, typename T2>   inline std::ostream& operator<<(std::ostream& os, const std::pair<T1, T2>& p) {     return os <<  (  << p.first <<  ,   << p.second <<  ) ;   }   template <typename T>   inline std::ostream& operator<<(std::ostream& os, const std::vector<T>& v) {     bool first = true;     os <<  [ ;     for (unsigned int i = 0; i < v.size(); i++) {       if (!first) os <<  ,  ;       os << v[i];       first = false;     }     return os <<  ] ;   }   template <typename T>   inline std::ostream& operator<<(std::ostream& os, const std::set<T>& v) {     bool first = true;     os <<  [ ;     for (typename std::set<T>::const_iterator ii = v.begin(); ii != v.end();          ++ii) {       if (!first) os <<  ,  ;       os << *ii;       first = false;     }     return os <<  ] ;   }   template <typename T1, typename T2>   inline std::ostream& operator<<(std::ostream& os, const std::map<T1, T2>& v) {     bool first = true;     os <<  [ ;     for (typename std::map<T1, T2>::const_iterator ii = v.begin(); ii != v.end();          ++ii) {       if (!first) os <<  ,  ;       os << *ii;       first = false;     }     return os <<  ] ;   }   struct debugger {     bool first;     debugger() { first = true; }     template <typename T>     debugger& operator,(const T& v) {       if (!first) cout <<  ,  ;       cout << v;       first = false;       return *this;     }   };   long long n;   long long arr[10000000];   long long solve() {     vector<long long> st;     long long mx = 0;     for (long long i = 0; i < n; i++) {       while (!st.empty() && st.back() < arr[i]) st.pop_back();       st.push_back(arr[i]);       if (st.size() >= 2) mx = max(mx, st[st.size() - 1] ^ st[st.size() - 2]);     }     return mx;   }   int32_t main(void) {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     cin >> n;     for (long long i = 0; i < n; i++) cin >> arr[i];     long long mx = solve();     reverse(arr, arr + n);     cout << max(mx, solve());   }   