Language: C++

int main(void){
	string s;
	cin >> s;

	if (s.size() < 4){
		cout << 0 << endl;
		return 0;
	}

	string a[100];
	for (ll i = 0;i < 100;i++){
		ll tmp = 2019 * (i+1);
		a[i] = to_string(tmp);
	}

	ll ans = 0;
	for (ll i = 0;i < 100 && a[i].size() <= s.size();i++){
		for (ll j = 0;j < s.size()-a[i].size()+1;j++){
			string str = s.substr(j, a[i].size());
			if (str == a[i]){
				ans++;
			}
		}
	}

	cout << ans << endl;
	return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:2:9: error: 'string' was not declared in this scope
    2 |         string s;
      |         ^~~~~~
a.cc:3:9: error: 'cin' was not declared in this scope
    3 |         cin >> s;
      |         ^~~
a.cc:3:16: error: 's' was not declared in this scope
    3 |         cin >> s;
      |                ^
a.cc:6:17: error: 'cout' was not declared in this scope
    6 |                 cout << 0 << endl;
      |                 ^~~~
a.cc:6:30: error: 'endl' was not declared in this scope
    6 |                 cout << 0 << endl;
      |                              ^~~~
a.cc:10:15: error: expected ';' before 'a'
   10 |         string a[100];
      |               ^~
      |               ;
a.cc:11:14: error: 'll' was not declared in this scope
   11 |         for (ll i = 0;i < 100;i++){
      |              ^~
a.cc:11:23: error: 'i' was not declared in this scope
   11 |         for (ll i = 0;i < 100;i++){
      |                       ^
a.cc:12:19: error: expected ';' before 'tmp'
   12 |                 ll tmp = 2019 * (i+1);
      |                   ^~~~
      |                   ;
a.cc:13:17: error: 'a' was not declared in this scope
   13 |                 a[i] = to_string(tmp);
      |                 ^
a.cc:13:34: error: 'tmp' was not declared in this scope
   13 |                 a[i] = to_string(tmp);
      |                                  ^~~
a.cc:13:24: error: 'to_string' was not declared in this scope
   13 |                 a[i] = to_string(tmp);
      |                        ^~~~~~~~~
a.cc:16:9: error: 'll' was not declared in this scope
   16 |         ll ans = 0;
      |         ^~
a.cc:17:16: error: expected ';' before 'i'
   17 |         for (ll i = 0;i < 100 && a[i].size() <= s.size();i++){
      |                ^~
      |                ;
a.cc:17:23: error: 'i' was not declared in this scope
   17 |         for (ll i = 0;i < 100 && a[i].size() <= s.size();i++){
      |                       ^
a.cc:17:34: error: 'a' was not declared in this scope
   17 |         for (ll i = 0;i < 100 && a[i].size() <= s.size();i++){
      |                                  ^
a.cc:18:24: error: expected ';' before 'j'
   18 |                 for (ll j = 0;j < s.size()-a[i].size()+1;j++){
      |                        ^~
      |                        ;
a.cc:18:31: error: 'j' was not declared in this scope
   18 |                 for (ll j = 0;j < s.size()-a[i].size()+1;j++){
      |                               ^
a.cc:19:31: error: expected ';' before 'str'
   19 |                         string str = s.substr(j, a[i].size());
      |                               ^~~~
      |                               ;
a.cc:20:29: error: 'str' was not declared in this scope; did you mean 'std'?
   20 |                         if (str == a[i]){
      |                             ^~~
      |                             std
a.cc:21:33: error: 'ans' was not declared in this scope
   21 |                                 ans++;
      |                                 ^~~
a.cc:26:9: error: 'cout' was not declared in this scope
   26 |         cout << ans << endl;
      |         ^~~~
a.cc:26:17: error: 'ans' was not declared in this scope
   26 |         cout << ans << endl;
      |                 ^~~
a.cc:26:24: error: 'endl' was not declared in this scope
   26 |         cout << ans << endl;
      |                        ^~~~