Language: C++

#include "bits/stdc++.h"
#define ALL(x) x.begin(),x.end()
#define rep(i,n) for(int i=0;i<n;++i)

using namespace std;
typedef ll long long;


template<typename T>
T gcd(T a, T b){
   if (a%b == 0){
       return(b);
   }
   else{
       return(gcd(b, a%b));
   }
}

template<typename T>
T lcm(T a,T b){
    return a/gcd(a,b)/b;
}

int main(){
    ll N; cin >> N;
    map<ll, ll> m{};
    for(ll i=0;i<N;i++) {
        ll n; cin >> n; m[n]++;
    }
    
    int count=0;
    ll a=0; ll b=0;
    map<ll, ll> ::reverse_iterator i;
    for(i=m.rbegin();i!= m.rend();i++){
        if(i->second>=4){
            if(a==0) {a=i->first; b=i->first;}
            else{ b=i->first;}
            count=2;
        }else if(i->second>=2){
            if(count==0) a=i->first;
            else b = i->first;
            count++;
        }
        if(count==2) break;
    }
    cout << a*b << endl;
}
/*

*/

Compiler output:
a.cc:6:9: error: 'll' does not name a type
    6 | typedef ll long long;
      |         ^~
a.cc: In function 'int main()':
a.cc:25:5: error: 'll' was not declared in this scope
   25 |     ll N; cin >> N;
      |     ^~
a.cc:25:18: error: 'N' was not declared in this scope
   25 |     ll N; cin >> N;
      |                  ^
a.cc:26:15: error: template argument 3 is invalid
   26 |     map<ll, ll> m{};
      |               ^
a.cc:26:15: error: template argument 4 is invalid
a.cc:27:11: error: expected ';' before 'i'
   27 |     for(ll i=0;i<N;i++) {
      |           ^~
      |           ;
a.cc:27:16: error: 'i' was not declared in this scope
   27 |     for(ll i=0;i<N;i++) {
      |                ^
a.cc:28:11: error: expected ';' before 'n'
   28 |         ll n; cin >> n; m[n]++;
      |           ^~
      |           ;
a.cc:28:22: error: 'n' was not declared in this scope
   28 |         ll n; cin >> n; m[n]++;
      |                      ^
a.cc:32:7: error: expected ';' before 'a'
   32 |     ll a=0; ll b=0;
      |       ^~
      |       ;
a.cc:32:15: error: expected ';' before 'b'
   32 |     ll a=0; ll b=0;
      |               ^~
      |               ;
a.cc:33:15: error: template argument 3 is invalid
   33 |     map<ll, ll> ::reverse_iterator i;
      |               ^
a.cc:33:15: error: template argument 4 is invalid
a.cc:33:36: error: expected initializer before 'i'
   33 |     map<ll, ll> ::reverse_iterator i;
      |                                    ^
a.cc:34:9: error: 'i' was not declared in this scope
   34 |     for(i=m.rbegin();i!= m.rend();i++){
      |         ^
a.cc:34:13: error: request for member 'rbegin' in 'm', which is of non-class type 'int'
   34 |     for(i=m.rbegin();i!= m.rend();i++){
      |             ^~~~~~
a.cc:34:28: error: request for member 'rend' in 'm', which is of non-class type 'int'
   34 |     for(i=m.rbegin();i!= m.rend();i++){
      |                            ^~~~
a.cc:36:16: error: 'a' was not declared in this scope
   36 |             if(a==0) {a=i->first; b=i->first;}
      |                ^
a.cc:36:35: error: 'b' was not declared in this scope
   36 |             if(a==0) {a=i->first; b=i->first;}
      |                                   ^
a.cc:37:19: error: 'b' was not declared in this scope
   37 |             else{ b=i->first;}
      |                   ^
a.cc:40:26: error: 'a' was not declared in this scope
   40 |             if(count==0) a=i->first;
      |                          ^
a.cc:41:18: error: 'b' was not declared in this scope
   41 |             else b = i->first;
      |                  ^
a.cc:46:13: error: 'a' was not declared in this scope
   46 |     cout << a*b << endl;
      |             ^
a.cc:46:15: error: 'b' was not declared in this scope
   46 |     cout << a*b << endl;
      |               ^