Language: C++

#include <bits/stdc++.h>
using namespace std;

#define REP(i, m, n) for (long i = (m); i < (long)(n); i++)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, x) for (int i = ((int)(x)-1); i >= 0; i--)
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define mp make_pair
typedef long long ll;
const ll INF = 1LL << 60;
const ll mod = 1e9 + 7;
template <class T>
bool chmax(T &a, const T &b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
bool chmin(T &a, const T &b)
{
    if (b < a)
    {
        a = b;
        return 1;
    }
    return 0;
}

ll modpow(ll a, ll p)
{
    if (p == 0)
        return 1;
    if (!(p % 2))
    {
        ll halfP = p / 2;
        ll half = modpow(a, p);
        return half * half % mod;
    }
    else
    {
        return a * modpow(a, p - 1) % mod;
    }
}

ll comb(int a, int b)
{
    if (b > a - b)
        return comb(a, a - b);
    ll ansMul = 1;
    ll ansDiv = 1;
    for (int i = 0; i < b; i++)
    {
        ansMul *= a - i;
        ansDiv *= i + 1;
        ansMul %= mod;
        ansDiv %= mod;
    }
    ll ans = ansMul * modpow(ansDiv, mod - 2) % mod;
    return ans;
}

int main() {
    ll l, r; cin >> l >> r;
    int res = 2020;
    REP(i, l, min(r, l+2019*2)) {
        REP(j, i+1, min(r+1, l+2020*2)) {
            //cout << i << ' ' << j << ' ' << i *j % 2019;
            res = min(res, (i * j) % 2019);
        }
    }
    cout << res << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:73:22: error: no matching function for call to 'min(int&, long int)'
   73 |             res = min(res, (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: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:73:22: note:   deduced conflicting types for parameter 'const _Tp' ('int' and 'long int')
   73 |             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:
/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:73:22: note:   mismatched types 'std::initializer_list<_Tp>' and 'int'
   73 |             res = min(res, (i * j) % 2019);
      |                   ~~~^~~~~~~~~~~~~~~~~~~~~