Language: C++

#include<bits/stdc++.h>
using namespace std;
using long long =ll;
const int mod = 1000000007;
#define rep(i, n) for(int i = 0; i < (n); i++)

int int_len(int n) {
  int s=0;
  while(n!=0) s++, n/=10;
  return s;
}

int int_sum(int n) {
  int m=0,s=0,a=n;
  while(a!=0) s++, a/=10;
  for(int i=s-1;i>=0;i--) m+=n/((int)pow(10,i))-(n/((int)pow(10,i+1)))*10;
  return m;
}






int ggcd(int a,int b)
{
 
  int r, tmp;
 
  
 
  /* 自然数 a > b を確認・入替 */
  if(a<b){
    tmp = a;
    a = b;
    b = tmp;
  }
 
  /* ユークリッドの互除法 */
  r = a % b;
  while(r!=0){
    a = b;
    b = r;
    r = a % b;
  }
 
 
 
  return b;
}







int fac(int n){
  int m=1;
  while(n>=1) m*=n,n--;
  return m;
}

int vec_sum(vector<int> v){
  int n=0;
  for(int i=0;i<v.size();i++) n+=v[i];
  return n;
}
///////////////////////////
int main() {
  int n;
  cin>>n;
  vector<ll> v(n);
  set<ll> st;
  rep(i,n){
    cin>>v[i];
    st.insert(v[i]);
  }
  if(v.size()-st.size()<2){
    cout<<0<<endl;
  }else{
    ll w,h,k=-1,count=0,ans=1;
    sort(v.begin(),v.end(),greater<int>());
    rep(i,n-1){
      if(count==2){
        cout<<ans<<endl;
        return 0;
      }
      if(k==i+1){
        k=-1;
        continue;
      }
      if(v[i]==v[i+1]){
        ans*=v[i];
        k=i+1;
        count++;
      }
      
    }
    
    
    
    
  }
}
///////////////////////////

Compiler output:
a.cc:3:7: error: expected nested-name-specifier before 'long'
    3 | using long long =ll;
      |       ^~~~
a.cc: In function 'int main()':
a.cc:73:10: error: 'll' was not declared in this scope
   73 |   vector<ll> v(n);
      |          ^~
a.cc:73:12: error: template argument 1 is invalid
   73 |   vector<ll> v(n);
      |            ^
a.cc:73:12: error: template argument 2 is invalid
a.cc:74:9: error: template argument 2 is invalid
   74 |   set<ll> st;
      |         ^
a.cc:74:9: error: template argument 3 is invalid
a.cc:76:11: error: invalid types 'int[int]' for array subscript
   76 |     cin>>v[i];
      |           ^
a.cc:77:8: error: request for member 'insert' in 'st', which is of non-class type 'int'
   77 |     st.insert(v[i]);
      |        ^~~~~~
a.cc:77:16: error: invalid types 'int[int]' for array subscript
   77 |     st.insert(v[i]);
      |                ^
a.cc:79:8: error: request for member 'size' in 'v', which is of non-class type 'int'
   79 |   if(v.size()-st.size()<2){
      |        ^~~~
a.cc:79:18: error: request for member 'size' in 'st', which is of non-class type 'int'
   79 |   if(v.size()-st.size()<2){
      |                  ^~~~
a.cc:82:7: error: expected ';' before 'w'
   82 |     ll w,h,k=-1,count=0,ans=1;
      |       ^~
      |       ;
a.cc:83:12: error: request for member 'begin' in 'v', which is of non-class type 'int'
   83 |     sort(v.begin(),v.end(),greater<int>());
      |            ^~~~~
a.cc:83:22: error: request for member 'end' in 'v', which is of non-class type 'int'
   83 |     sort(v.begin(),v.end(),greater<int>());
      |                      ^~~
a.cc:85:15: error: invalid operands of types '<unresolved overloaded function type>' and 'int' to binary 'operator=='
   85 |       if(count==2){
      |          ~~~~~^~~
a.cc:86:15: error: 'ans' was not declared in this scope; did you mean 'abs'?
   86 |         cout<<ans<<endl;
      |               ^~~
      |               abs
a.cc:89:10: error: 'k' was not declared in this scope
   89 |       if(k==i+1){
      |          ^
a.cc:93:11: error: invalid types 'int[int]' for array subscript
   93 |       if(v[i]==v[i+1]){
      |           ^
a.cc:93:17: error: invalid types 'int[int]' for array subscript
   93 |       if(v[i]==v[i+1]){
      |                 ^
a.cc:94:9: error: 'ans' was not declared in this scope; did you mean 'abs'?
   94 |         ans*=v[i];
      |         ^~~
      |         abs
a.cc:94:15: error: invalid types 'int[int]' for array subscript
   94 |         ans*=v[i];
      |               ^
a.cc:95:9: error: 'k' was not declared in this scope
   95 |         k=i+1;
      |         ^
a.cc:96:14: error: no post-increment operator for type
   96 |         count++;
      |              ^~