Language: C++

#include <bits/stdc++.h>
#include <math.h>
#include <cmath>
using namespace std;
bool is_int_lround(double x){
  return std::lround(x)==x;
}
int ketasuu(int x){
  int n=0;
  while(x>0){
    x /=10 ;
    n ++;
  }
  return n;
}

int main(){
  long long L,R;
  cin >> L >> R;
  vector<int> num(R-L+1);
  for(long long i=0; i<R-L+1;i++){
    num[i]=(L+i)%2019;
  }
  sort(num.begin(),num.end());
  while(num[0]*num*[1] < 2019){
    num[0]*num[1] = num[0]*num[1]%2019; 
  }
  cout <<num[0]*num[1]<<endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:25:15: error: no match for 'operator*' (operand types are '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'} and 'std::vector<int>')
   25 |   while(num[0]*num*[1] < 2019){
In file included from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127,
                 from a.cc:1:
/usr/include/c++/14/complex:400:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const complex<_Tp>&)'
  400 |     operator*(const complex<_Tp>& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:400:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::complex<_Tp>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/complex:409:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const complex<_Tp>&, const _Tp&)'
  409 |     operator*(const complex<_Tp>& __x, const _Tp& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:409:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::complex<_Tp>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/complex:418:5: note: candidate: 'template<class _Tp> std::complex<_Tp> std::operator*(const _Tp&, const complex<_Tp>&)'
  418 |     operator*(const _Tp& __x, const complex<_Tp>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/complex:418:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   'std::vector<int>' is not derived from 'const std::complex<_Tp>'
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
In file included from /usr/include/c++/14/valarray:605,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:166:
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   'std::vector<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::_Expr<_Dom1, typename _Dom1::value_type>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note: candidate: 'template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__multiplies, typename _Dom1::value_type>::result_type> std::operator*(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)'
  407 |     _DEFINE_EXPR_BINARY_OPERATOR(*, struct std::__multiplies)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/valarray_after.h:407:5: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   'std::vector<int>' is not derived from 'const std::_Expr<_Dom1, typename _Dom1::value_type>'
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::valarray<_Tp>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   mismatched types 'const std::valarray<_Tp>' and '__gnu_cxx::__alloc_traits<std::allocator<int>, int>::value_type' {aka 'int'}
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
/usr/include/c++/14/valarray:1198:1: note: candidate: 'template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__multiplies, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__multiplies, _Tp>::result_type> std::operator*(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)'
 1198 | _DEFINE_BINARY_OPERATOR(*, __multiplies)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/valarray:1198:1: note:   template argument deduction/substitution failed:
a.cc:25:16: note:   'std::vector<int>' is not derived from 'const std::valarray<_Tp>'
   25 |   while(num[0]*num*[1] < 2019){
      |                ^~~
a.cc:25:21: error: expected identifier before numeric constant
   25 |   while(num[0]*num*[1] < 2019){
      |                     ^
a.cc:25:26: error: expected identifier before numeric constant
   25 |   while(num[0]*num*[1] < 2019){
      |                          ^~~~
a.cc:25:26: error: expected '>' before numeric constant
a.cc: In lambda function:
a.cc:25:30: error: expected '{' before ')' token
   25 |   while(num[0]*num*[1] < 2019){
      |                              ^
a.cc: In function 'int main()':
a.cc:26:11: error: lvalue required as left operand of assignment
   26 |     num[0]*num[1] = num[0]*num[1]%2019;