Language: C++

#include <iostream>
#include <cstdio>
#include <cstdint>
#include <algorithm>

using namespace std;

int main()
{
    u_int64_t L, R;
    cin >> L >> R;

    u_int64_t len = min(
        R - L + 1,
        (R - L + 1) % 2019LL + 2019LL);

    u_int64_t m = 2019LL;
    for (u_int64_t i = 0; i < len - 1LL; i++)
    {
        for (u_int64_t j = i + 1LL; j < len; j++)
        {
            u_int64_t l = L + i;
            u_int64_t r = L + j;
            u_int64_t prod = l * r % 2019LL;

            m = min(m, prod);
        }
    }

    cout << m << endl;

    return 0;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:13:24: error: no matching function for call to 'min(u_int64_t, long long unsigned int)'
   13 |     u_int64_t len = min(
      |                     ~~~^
   14 |         R - L + 1,
      |         ~~~~~~~~~~      
   15 |         (R - L + 1) % 2019LL + 2019LL);
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:51,
                 from /usr/include/c++/14/bits/locale_classes.h:40,
                 from /usr/include/c++/14/bits/ios_base.h:41,
                 from /usr/include/c++/14/ios:44,
                 from /usr/include/c++/14/ostream:40,
                 from /usr/include/c++/14/iostream:41,
                 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:13:24: note:   deduced conflicting types for parameter 'const _Tp' ('long unsigned int' and 'long long unsigned int')
   13 |     u_int64_t len = min(
      |                     ~~~^
   14 |         R - L + 1,
      |         ~~~~~~~~~~      
   15 |         (R - L + 1) % 2019LL + 2019LL);
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/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,
                 from a.cc:4:
/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:13:24: note:   mismatched types 'std::initializer_list<_Tp>' and 'long unsigned int'
   13 |     u_int64_t len = min(
      |                     ~~~^
   14 |         R - L + 1,
      |         ~~~~~~~~~~      
   15 |         (R - L + 1) % 2019LL + 2019LL);
      |         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~