Language: C++

include<bits/stdc++.h>
using namespace std;
 
#define fast ios_base::sync_with_stdio(0)
 
typedef long long LL;
typedef vector<LL>vll;
typedef map<LL, int>mplli;
 
vll v;
mplli mp;
 
set<LL>st;
 
int main()
{
    fast;
    int N;
    cin >> N;
    int i;
    for(i=0; i<N; i++)
    {
        LL x;
        cin >> x;
        st.insert(x);
        mp[x]++;
    }
 
    set<LL>::iterator it;
 
    for(it=st.begin(); it!=st.end(); it++)
    {
       // cout << *it << "; ";
        v.push_back(*it);
    }
 
    int len = v.size();
 
    LL mul = 1;
    int cnt = 0;
 
    for(i=len-1; i>=0; i--)
    {
        if(mp[v[i]] >= 2)
        {
            mul *= v[i];
            //cout << mul << "; ";
            cnt+=1;
        }
 
        if(cnt == 2) break;
    }
 
    if(cnt == 2) cout << mul << "\n";
    else
    {
        mul = 1;
        cnt = 0;
 
        for(i=0; i<len; i++)
        {
            if(mp[v[i]] >= 3)
            {
                cnt = 1;
                mul = v[i] * v[i];
                break;
            }
        }
 
        if(cnt == 1) cout << mul << "\n";
        else cout << "0\n";
    }
 
    return 0;
}

Compiler output:
a.cc:1:1: error: 'include' does not name a type
    1 | include<bits/stdc++.h>
      | ^~~~~~~
a.cc:7:9: error: 'vector' does not name a type
    7 | typedef vector<LL>vll;
      |         ^~~~~~
a.cc:8:9: error: 'map' does not name a type
    8 | typedef map<LL, int>mplli;
      |         ^~~
a.cc:10:1: error: 'vll' does not name a type
   10 | vll v;
      | ^~~
a.cc:11:1: error: 'mplli' does not name a type
   11 | mplli mp;
      | ^~~~~
a.cc:13:1: error: 'set' does not name a type
   13 | set<LL>st;
      | ^~~
a.cc: In function 'int main()':
a.cc:4:14: error: 'ios_base' has not been declared
    4 | #define fast ios_base::sync_with_stdio(0)
      |              ^~~~~~~~
a.cc:17:5: note: in expansion of macro 'fast'
   17 |     fast;
      |     ^~~~
a.cc:19:5: error: 'cin' was not declared in this scope
   19 |     cin >> N;
      |     ^~~
a.cc:25:9: error: 'st' was not declared in this scope; did you mean 'std'?
   25 |         st.insert(x);
      |         ^~
      |         std
a.cc:26:9: error: 'mp' was not declared in this scope
   26 |         mp[x]++;
      |         ^~
a.cc:29:5: error: 'set' was not declared in this scope
   29 |     set<LL>::iterator it;
      |     ^~~
a.cc:29:11: error: expected primary-expression before '>' token
   29 |     set<LL>::iterator it;
      |           ^
a.cc:29:14: error: '::iterator' has not been declared
   29 |     set<LL>::iterator it;
      |              ^~~~~~~~
a.cc:31:9: error: 'it' was not declared in this scope; did you mean 'i'?
   31 |     for(it=st.begin(); it!=st.end(); it++)
      |         ^~
      |         i
a.cc:31:12: error: 'st' was not declared in this scope; did you mean 'std'?
   31 |     for(it=st.begin(); it!=st.end(); it++)
      |            ^~
      |            std
a.cc:34:9: error: 'v' was not declared in this scope
   34 |         v.push_back(*it);
      |         ^
a.cc:37:15: error: 'v' was not declared in this scope
   37 |     int len = v.size();
      |               ^
a.cc:44:12: error: 'mp' was not declared in this scope
   44 |         if(mp[v[i]] >= 2)
      |            ^~
a.cc:54:18: error: 'cout' was not declared in this scope
   54 |     if(cnt == 2) cout << mul << "\n";
      |                  ^~~~
a.cc:62:16: error: 'mp' was not declared in this scope
   62 |             if(mp[v[i]] >= 3)
      |                ^~
a.cc:70:22: error: 'cout' was not declared in this scope
   70 |         if(cnt == 1) cout << mul << "\n";
      |                      ^~~~
a.cc:71:14: error: 'cout' was not declared in this scope
   71 |         else cout << "0\n";
      |              ^~~~