Language: C++

#include <iostream> // cin, cout, cerr, clog
#include <algorithm> // min, max, sort, swap
#include <numeric> // iota, accumulate, inner_product
#include <climits> // INT_MIN, LLONG_MIN
#include <cmath> // long, trig, pow
#include <string> // string, stoi, to_string
#include <vector> // vector
#include <queue> // queue, priority_queue
#include <stack> // stack
#include <deque> // deque
#include <map> // key-value pairs sorted by keys
#include <set> // set
#include <unordered_map> // hashed by keys
#include <unordered_set> // hashed by keys
#include <iomanip> // cout<<setprecision(n)

using namespace std;

typedef long long ll;
const ll mod = 1000000007;
const ll INF = mod * mod;

int main() {
	ll l, r;
	cin >> l >> r;
	ll res = 1e10;
	for (int i = l; i <= min(2019 + l, r); i++) {
		for (int j = i + 1; j <= min(2019 + l, r); j++) {
			res = min(res, i * j % 2019);
		}
	}
	cout << res << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:29:34: error: no matching function for call to 'min(ll&, int)'
   29 |                         res = min(res, i * j % 2019);
      |                               ~~~^~~~~~~~~~~~~~~~~~~
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:29:34: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   29 |                         res = min(res, i * j % 2019);
      |                               ~~~^~~~~~~~~~~~~~~~~~~
/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:2:
/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:29:34: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   29 |                         res = min(res, i * j % 2019);
      |                               ~~~^~~~~~~~~~~~~~~~~~~