Language: C++

#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define REP(i,a,b) for (int i = a; i < (b); ++i)
#define all(x) (x).begin(),(x).end()
#define YY cout << "Yes" << endl;
#define NN cout << "No" << endl;
#define ve vector
const int INF = 1000000007;
typedef long long ll;
using namespace std;
using Graph = vector<vector<int>>;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
ll gcd(ll a, ll b) { return b ? gcd(b, a%b) : a; }
ll lcm(ll a, ll b) { return (a * b) / gcd(a,b); }
// *max_element(all(d));
class UnionFind{
  private:
    vector<int>par;
  public:
    UnionFind(int n):par(n,-1){}
    int root(int x){
      if(par[x] < 0)return x;
      return par[x] = root(par[x]);
    }
    bool unite(int x,int y){
      x = root(x); y = root(y);
      if (x == y) return false;
      if (par[x] > par[y]) swap(x, y);
      par[x] += par[y];
      par[y] = x;
      return true;
    }
    bool same(int x,int y){
      return root(x) == root(y);
    }
    int size(int x) {
      return -par[root(x)];
    }
};
int solve(){ 
  ll l,r;
  cin >> l >> r;
  ll ans = INF;
  ll cnt = 0;
  REP(i,l,min(r,l+2019)+1)REP(j,i+1,min(r,l+2019)+1)ans = min(ans,i * j % 2019);
  cout << ans << endl;
  return 0; 
}
int main(){
  // ios::sync_with_stdio(false);cin.tie(nullptr);
  // cout << fixed;cout << setprecision(16) << endl; 
  solve();
  return 0;
} 

Compiler output:
a.cc: In function 'int solve()':
a.cc:47:62: error: no matching function for call to 'min(ll&, int)'
   47 |   REP(i,l,min(r,l+2019)+1)REP(j,i+1,min(r,l+2019)+1)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:2:
/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:47:62: note:   deduced conflicting types for parameter 'const _Tp' ('long long int' and 'int')
   47 |   REP(i,l,min(r,l+2019)+1)REP(j,i+1,min(r,l+2019)+1)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:47:62: note:   mismatched types 'std::initializer_list<_Tp>' and 'long long int'
   47 |   REP(i,l,min(r,l+2019)+1)REP(j,i+1,min(r,l+2019)+1)ans = min(ans,i * j % 2019);
      |                                                           ~~~^~~~~~~~~~~~~~~~~~