Language: C++

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

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<string, string> pss;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vii;
typedef vector<ll> vl;
typedef vector<vl> vvl;

double EPS=1e-9;
int INF=1000000005;
long long INFF=1000000000000000005ll;
double PI=acos(-1);
int dirx[8]={ -1, 0, 0, 1, -1, -1, 1, 1 };
int diry[8]={ 0, 1, -1, 0, -1, 1, -1, 1 };
const ll MOD = 1000000007;

ll sum() { return 0; }
template<typename T, typename... Args>
T sum(T a, Args... args) { return a + sum(args...); }

#define DEBUG fprintf(stderr, "====TESTING====\n")
#define VALUE(x) cerr << "The value of " << #x << " is " << x << endl
#define OUT(x) cout << x << endl
#define OUTH(x) cout << x << " "
#define debug(...) fprintf(stderr, __VA_ARGS__)
#define READ(x) for(auto &(z):x) cin >> z;
#define FOR(a, b, c) for (int(a)=(b); (a) < (c); ++(a))
#define FORN(a, b, c) for (int(a)=(b); (a) <= (c); ++(a))
#define FORD(a, b, c) for (int(a)=(b); (a) >= (c); --(a))
#define FORSQ(a, b, c) for (int(a)=(b); (a) * (a) <= (c); ++(a))
#define FORC(a, b, c) for (char(a)=(b); (a) <= (c); ++(a))
#define EACH(a, b) for (auto&(a) : (b))
#define REP(i, n) FOR(i, 0, n)
#define REPN(i, n) FORN(i, 1, n)
#define MAX(a, b) a=max(a, b)
#define MIN(a, b) a=min(a, b)
#define SQR(x) ((ll)(x) * (x))
#define RESET(a, b) memset(a, b, sizeof(a))
#define fi first
#define se second
#define mp make_pair
#define pb push_back
#define ALL(v) v.begin(), v.end()
#define ALLA(arr, sz) arr, arr + sz
#define SIZE(v) (int)v.size()
#define SORT(v) sort(ALL(v))
#define REVERSE(v) reverse(ALL(v))
#define SORTA(arr, sz) sort(ALLA(arr, sz))
#define REVERSEA(arr, sz) reverse(ALLA(arr, sz))
#define PERMUTE next_permutation
#define TC(t) while (t--)
#define FAST_INP  ios_base::sync_with_stdio(false);cin.tie(NULL)
#define what_is(x) cerr << #x << " is " << x << endl;

void solve() {

}

int main()
{
    FAST_INP;
//    #ifndef ONLINE_JUDGE
//    freopen("input.txt","r", stdin);
//    freopen("output.txt","w", stdout);
//    #endif

//    int tc; cin >> tc;
//    TC(tc) solve();
	int l, r;
	cin >> l >> r;
//	if((l-1)/2019!=r/2019) {
	if(r-l>=2018)
		OUT(0);
		return 0;
	}
	l%=2019, r%=2019;
	int ans=2018;
	FORN(i,l,r){
		FORN(j,i+1,r){
			MIN(ans, (i*j)%2019);
		}
	}
	OUT(ans);
    return 0;
}

Compiler output:
a.cc:81:9: error: 'l' does not name a type; did you mean 'vl'?
   81 |         l%=2019, r%=2019;
      |         ^
      |         vl
a.cc:33:23: error: expected unqualified-id before 'for'
   33 | #define FORN(a, b, c) for (int(a)=(b); (a) <= (c); ++(a))
      |                       ^~~
a.cc:83:9: note: in expansion of macro 'FORN'
   83 |         FORN(i,l,r){
      |         ^~~~
a.cc:33:44: error: expected constructor, destructor, or type conversion before '<=' token
   33 | #define FORN(a, b, c) for (int(a)=(b); (a) <= (c); ++(a))
      |                                            ^~
a.cc:83:9: note: in expansion of macro 'FORN'
   83 |         FORN(i,l,r){
      |         ^~~~
a.cc:33:52: error: expected unqualified-id before '++' token
   33 | #define FORN(a, b, c) for (int(a)=(b); (a) <= (c); ++(a))
      |                                                    ^~
a.cc:83:9: note: in expansion of macro 'FORN'
   83 |         FORN(i,l,r){
      |         ^~~~
a.cc:28:16: error: 'cout' does not name a type
   28 | #define OUT(x) cout << x << endl
      |                ^~~~
a.cc:88:9: note: in expansion of macro 'OUT'
   88 |         OUT(ans);
      |         ^~~
a.cc:89:5: error: expected unqualified-id before 'return'
   89 |     return 0;
      |     ^~~~~~
a.cc:90:1: error: expected declaration before '}' token
   90 | }
      | ^