Language: C++

#include <bits/stdc++.h>
using namespace std;
 
int main(){
  long long L,R;
  cin >> L >> R;
  for(int i=1;i<1000000:i++){
    if(L<=2019*i&&2019*i<=R){
      cout << "0" << endl;
      return 0;
    }
  }
  long long ans=2020;
  for(int i=L;i<R;i++){
    for(int j=i+1;j<=R;j++){
      int num=(i*j)%2019;
      ans=min(ans,num);
    }
  }
  cout << ans << endl;
}
  

Compiler output:
a.cc: In function 'int main()':
a.cc:7:15: warning: range-based 'for' loops with initializer only available with '-std=c++20' or '-std=gnu++20' [-Wc++20-extensions]
    7 |   for(int i=1;i<1000000:i++){
      |               ^
a.cc:7:24: error: expected ';' before ':' token
    7 |   for(int i=1;i<1000000:i++){
      |                        ^
      |                        ;
a.cc:14:3: error: expected primary-expression before 'for'
   14 |   for(int i=L;i<R;i++){
      |   ^~~
a.cc:13:22: error: expected ')' before 'for'
   13 |   long long ans=2020;
      |                      ^
      |                      )
   14 |   for(int i=L;i<R;i++){
      |   ~~~                 
a.cc:7:6: note: to match this '('
    7 |   for(int i=1;i<1000000:i++){
      |      ^
a.cc:17:14: error: no matching function for call to 'min(long long int&, int&)'
   17 |       ans=min(ans,num);
      |           ~~~^~~~~~~~~
In file included from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_algobase.h:233:5: note: candidate: 'template<class _Tp> constexpr const _Tp& std::min(const _Tp&, const _Tp&)'
  233 |     min(const _Tp& __a, const _Tp& __b)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:233:5: note:   template argument deduction/substitution failed:
a.cc:17:14: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   17 |       ans=min(ans,num);
      |           ~~~^~~~~~~~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note: candidate: 'template<class _Tp, class _Compare> constexpr const _Tp& std::min(const _Tp&, const _Tp&, _Compare)'
  281 |     min(const _Tp& __a, const _Tp& __b, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algobase.h:281:5: note:   candidate expects 3 arguments, 2 provided
In file included from /usr/include/c++/14/algorithm:61:
/usr/include/c++/14/bits/stl_algo.h:5686:5: note: candidate: 'template<class _Tp> constexpr _Tp std::min(initializer_list<_Tp>)'
 5686 |     min(initializer_list<_Tp> __l)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5686:5: note:   candidate expects 1 argument, 2 provided
/usr/include/c++/14/bits/stl_algo.h:5696:5: note: candidate: 'template<class _Tp, class _Compare> constexpr _Tp std::min(initializer_list<_Tp>, _Compare)'
 5696 |     min(initializer_list<_Tp> __l, _Compare __comp)
      |     ^~~
/usr/include/c++/14/bits/stl_algo.h:5696:5: note:   template argument deduction/substitution failed:
a.cc:17:14: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   17 |       ans=min(ans,num);
      |           ~~~^~~~~~~~~
a.cc:20:11: error: 'ans' was not declared in this scope; did you mean 'abs'?
   20 |   cout << ans << endl;
      |           ^~~
      |           abs