func_code_string: #include <bits/stdc++.h>   using namespace std;   using ll = long long;   using ld = long double;   namespace io {   template <class T>   void re(complex<T>& x);   template <class T1, class T2>   void re(pair<T1, T2>& p);   template <class T>   void re(vector<T>& a);   template <class T, size_t SZ>   void re(array<T, SZ>& a);   template <class T>   void re(T& x) {     cin >> x;   }   void re(double& x) {     string t;     re(t);     x = stod(t);   }   void re(ld& x) {     string t;     re(t);     x = stold(t);   }   template <class T, class... Ts>   void re(T& t, Ts&... ts) {     re(t);     re(ts...);   }   template <class T>   void re(complex<T>& x) {     T a, b;     re(a, b);     x = {a, b};   }   template <class T1, class T2>   void re(pair<T1, T2>& p) {     re(p.f, p.s);   }   template <class T>   void re(vector<T>& a) {     for (int i = (0) - (1 - 2 * (0 > ((int)a.size())) < 0);          (1 - 2 * (0 > ((int)a.size()))) > 0 ? i < (((int)a.size()))                                              : i >= (((int)a.size()));          i += (1 - 2 * (0 > ((int)a.size()))))       re(a[i]);   }   template <class T, size_t SZ>   void re(array<T, SZ>& a) {     for (int i = (0) - (1 - 2 * (0 > SZ) < 0);          (1 - 2 * (0 > SZ)) > 0 ? i < (SZ) : i >= (SZ); i += (1 - 2 * (0 > SZ)))       re(a[i]);   }   void pr(int x) { cout << x; }   void pr(long x) { cout << x; }   void pr(ll x) { cout << x; }   void pr(unsigned x) { cout << x; }   void pr(unsigned long x) { cout << x; }   void pr(unsigned long long x) { cout << x; }   void pr(float x) { cout << x; }   void pr(double x) { cout << x; }   void pr(ld x) { cout << x; }   void pr(char x) { cout << x; }   void pr(const char* x) { cout << x; }   void pr(const string& x) { cout << x; }   void pr(bool x) { pr(x ?  true  :  false ); }   template <class T>   void pr(const complex<T>& x) {     cout << x;   }   template <class T1, class T2>   void pr(const pair<T1, T2>& x);   template <class T>   void pr(const T& x);   template <class T, class... Ts>   void pr(const T& t, const Ts&... ts) {     pr(t);     pr(ts...);   }   template <class T1, class T2>   void pr(const pair<T1, T2>& x) {     pr( { , x.f,  ,  , x.s,  } );   }   template <class T>   void pr(const T& x) {     pr( { );     bool fst = 1;     for (const auto& a : x) pr(!fst ?  ,   :   , a), fst = 0;     pr( } );   }   void ps() { pr(  n ); }   template <class T, class... Ts>   void ps(const T& t, const Ts&... ts) {     pr(t);     if (sizeof...(ts)) pr(   );     ps(ts...);   }   void pc() { pr( ] n ); }   template <class T, class... Ts>   void pc(const T& t, const Ts&... ts) {     pr(t);     if (sizeof...(ts)) pr( ,  );     pc(ts...);   }   }  // namespace io   using namespace io;   template <class T>   bool ckmin(T& a, const T& b) {     return b < a ? a = b, 1 : 0;   }   template <class T>   bool ckmax(T& a, const T& b) {     return a < b ? a = b, 1 : 0;   }   ll n;   unordered_map<ll, vector<int>> mp;   int find(int u, int v) {     if (u == v) return mp[v].size();     int n = ((int)mp[u].size()), m = ((int)mp[v].size());     int i = 0, j = 0, ans = 1, last;     bool cur = 0;     if (mp[u][i] < mp[v][j]) {       cur = 0;       last = mp[u][i];       i++;     } else {       cur = 1;       last = mp[v][j], j++;     }     while (i < n or j < m) {       if (i == n) {         if (cur == 0 and last < mp[v].back())           return ans + 1;         else           return ans;       } else if (j == m) {         if (cur == 1 and last < mp[u].back()) {           return ans + 1;         } else           return ans;       } else if (cur == 0) {         while (j < m and mp[v][j] < last) j++;         if (j < m) last = mp[v][j], ans++, j++, cur = 1;       } else {         while (i < n and mp[u][i] < last) i++;         if (i < n) last = mp[u][i], ans++, i++, cur = 0;       }     }     return ans;   }   int main() {     ios_base::sync_with_stdio(0);     cin.tie(NULL);     cout.tie(NULL);     re(n);     int a[n];     unordered_set<ll> st;     for (int i = (0) - (1 - 2 * (0 > n) < 0);          (1 - 2 * (0 > n)) > 0 ? i < (n) : i >= (n); i += (1 - 2 * (0 > n)))       re(a[i]), mp[a[i]].push_back(i), st.insert(a[i]);     int ans = 0;     vector<int> ss;     for (auto i : st) ss.push_back(i);     for (int ii = (0) - (1 - 2 * (0 > ((int)ss.size())) < 0);          (1 - 2 * (0 > ((int)ss.size()))) > 0 ? ii < (((int)ss.size()))                                               : ii >= (((int)ss.size()));          ii += (1 - 2 * (0 > ((int)ss.size())))) {       for (int jj = (ii) - (1 - 2 * (ii > ((int)ss.size())) < 0);            (1 - 2 * (ii > ((int)ss.size()))) > 0 ? jj < (((int)ss.size()))                                                  : jj >= (((int)ss.size()));            jj += (1 - 2 * (ii > ((int)ss.size())))) {         int i = ss[ii], j = ss[jj];         ckmax(ans, find(i, j));       }     }     ps(ans);   }   