Language: C++

#include <iostream>
#include <vector>
#include <algorithm>
#include <set>
#include <map>
#include <utility>
#include <tuple>
#include <string>
#include <cctype>
#include <cstdio>
#include <math.h>
using i8 = int8_t;
using u8 = uint8_t;
using i16 = int16_t;
using u16 = uint16_t;
using i32 = int32_t;
using u32 = uint32_t;
using i64 = int64_t;
using u64 = uint64_t;

using f32 = float;
using f64 = double;
using f80 = __float80;
constexpr i64 INF = 1'010'000'000'000'000'017LL;

constexpr i64 MOD = 1'000'000'007LL;

constexpr f64 EPS = 1e-12;

constexpr f64 PI = 3.14159265358979323846;
using namespace std;
#define rep(i, n) for (i64 i = 0; i < (int)(n); i++)
#define FOR(i, m, n) for (i64 i = m; i < n; i++)
#define SORT(x) sort(x.begin(), x.end())
#define REVE(x) reverse(x.begin(), x.end())
#define all(x) (x).begin(), (x).end()
#define fst first
#define mp make_pair
#define pb push_back
#define eb emplace_back
#define pob pop_back
#define sw swap
#define UP(x) transform(x.begin(), x.end(), x.begin(), ::toupper);
#define down(x) transform(x.begin(), x.end(), x.begin(), ::tolower);
using LL = long long;
using ULL = unsigned long long;
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;
}

int main()
{
  cin.tie(0);
ios::sync_with_stdio(false);
i64 L, R,w=2019;
cin >> L >> R;
if(R-L>=2019)return cout << 0,0;
for(ll j=l;j<=r;j++){
		FOR(i=1;i<j;i++)w=min(res,(i*j)%2019);
}
cout << c;
}

Compiler output:
a.cc:76:32: error: macro "FOR" requires 3 arguments, but only 1 given
   76 |                 FOR(i=1;i<j;i++)w=min(res,(i*j)%2019);
      |                                ^
a.cc:33:9: note: macro "FOR" defined here
   33 | #define FOR(i, m, n) for (i64 i = m; i < n; i++)
      |         ^~~
a.cc:13:12: error: 'uint8_t' does not name a type
   13 | using u8 = uint8_t;
      |            ^~~~~~~
a.cc:12:1: note: 'uint8_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
   11 | #include <math.h>
  +++ |+#include <cstdint>
   12 | using i8 = int8_t;
a.cc:15:13: error: 'uint16_t' does not name a type
   15 | using u16 = uint16_t;
      |             ^~~~~~~~
a.cc:15:13: note: 'uint16_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
a.cc:17:13: error: 'uint32_t' does not name a type
   17 | using u32 = uint32_t;
      |             ^~~~~~~~
a.cc:17:13: note: 'uint32_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
a.cc:19:13: error: 'uint64_t' does not name a type
   19 | using u64 = uint64_t;
      |             ^~~~~~~~
a.cc:19:13: note: 'uint64_t' is defined in header '<cstdint>'; this is probably fixable by adding '#include <cstdint>'
a.cc: In function 'int main()':
a.cc:75:5: error: 'll' was not declared in this scope; did you mean 'LL'?
   75 | for(ll j=l;j<=r;j++){
      |     ^~
      |     LL
a.cc:75:12: error: 'j' was not declared in this scope
   75 | for(ll j=l;j<=r;j++){
      |            ^
a.cc:75:15: error: 'r' was not declared in this scope
   75 | for(ll j=l;j<=r;j++){
      |               ^
a.cc:76:17: error: 'FOR' was not declared in this scope
   76 |                 FOR(i=1;i<j;i++)w=min(res,(i*j)%2019);
      |                 ^~~
a.cc:78:9: error: 'c' was not declared in this scope
   78 | cout << c;
      |         ^