Language: C++

//↓template↓

#include "bits/stdc++.h"
using namespace std;
#define Would
#define you
#define all(n)  n.begin(),n.end()
#define rall(n) n.rbegin(),n.rend()
typedef long long ll;
const ll INF = 1e18;
const ll MOD = 1e9 + 7;
const double pi = acos(-1);
const ll SIZE = 1 << 17;
int dx[] = { 1,0,-1,0 }, dy[] = { 0,1,0,-1 }, alp[30];
ll fac[200005], finv[200005], inv[200005];
vector<ll>dij;
struct edge { ll to, cost; };
vector<vector<edge> >G;

ll mod_pow(ll a, ll b) {
	ll res = 1, mul = a;
	for (int i = 0; i < 31; ++i) {
		if (b >> i & 1) {
			res *= mul;
			res %= MOD;
		}
		mul = (mul * mul) % MOD;
	}

	return res;
}

void addedge(int from, int to, int cost) {
	G[from].push_back({ to,cost });
	G[to].push_back({ from,cost });
}


template<typename T>
vector<T> make_v(size_t a) { return vector<T>(a); }

template<typename T, typename... Ts>
auto make_v(size_t a, Ts... ts) {
	return vector<decltype(make_v<T>(ts...))>(a, make_v<T>(ts...));
}

template<typename T, typename V>
typename enable_if<is_class<T>::value == 0>::type
fill_v(T &t, const V &v) { t = v; }

template<typename T, typename V>
typename enable_if<is_class<T>::value != 0>::type
fill_v(T &t, const V &v) {
	for (auto &e : t) fill_v(e, v);
}

template<typename T>
void outp(vector<T>v) {
	for (int i = 0; i < v.size(); ++i) {
		cout << v[i];
		if (i != v.size() - 1) { cout << " "; }
	}
}

//↑template↑



ll a, b, ans;
int main() {
	cin >> a >> b;
	a %= 2019; b %= 2019;
	for (int i = a; i <= b; ++i) {
		for (int j = i + 1; j <= b; ++j) {
			ans = min(ans, i*j % 2019);
		}
	}

	cout << ans << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:75:34: error: no matching function for call to 'min(ll&, int)'
   75 |                         ans = min(ans, i*j % 2019);
      |                               ~~~^~~~~~~~~~~~~~~~~
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:3:
/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:75:34: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   75 |                         ans = min(ans, 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:
/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:75:34: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   75 |                         ans = min(ans, i*j % 2019);
      |                               ~~~^~~~~~~~~~~~~~~~~