Language: C++

#include<bits/stdc++.h>
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
using namespace std;
template <typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using namespace std;
#define a_macro(args...) sum(args)
#define mp make_pair
#define eb emplace_back
#define mt make_tuple
#define fi first
#define se second
#define pb push_back
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))

typedef long long ll;
const ll mod = 1e9+7;

typedef tuple<int,int,int> State; // operator< defined
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<pii> vpi;
typedef vector<ll> vll;
typedef pair<ll, ll> pll;
typedef double ld;

/*---------------Matrix Multiplication-------------------
struct matrix {
  // N is the size of the matrix
  int m[N][N];
  matrix()
  {
     memset(m,0,sizeof(m));
  }
  matrix operator * (matrix b)
  {
     matrix c = matrix();
     for (int i = 0; i < N; ++i)
       for (int j = 0; j < N; ++j)
         for (int k = 0; k < N; ++k) 
           c.m[i][j] = (c.m[i][j] + 1LL * m[i][k] * b.m[k][j]) % M;
     return c;
  }
};
// Note that this multiplication method can be used to multiplying numbers,matrixes,etc....
matrix modPow(matrix m,int n)
{
  if ( n == 0 )
    return unit; // the unit matrix - that is 1 for principal diagonal , otherwise 0
  matrix half = modPow(m,n/2);
  matrix out = half * half;
  if ( n % 2 )
    out = out * m;
  return out; 
}
-----------------END-----------------------------------*/
int sum() { return 0; }

template<typename T, typename... Args>
auto sum(T a, Args... args) { return a + sum(args...); }
template<class T> bool uin(T &a,T b) {return a > b ? (a == b, true) : false; }
template<class T> bool uax(T &a,T b) {return a < b ? (a == b, true) : false; }

int main(int argc, const char** argv) {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.precision(10);
    cout << fixed;
#ifndef ONLINE_JUDGE
	freopen("input.txt","r",stdin);
	freopen("output.txt","w",stdout);
	freopen("error.txt","w",stderr);
#endif

	int i;
	string s;
	cin>>s;
	vector<int> multiple(101);
	for(i=1;i<=100;++i)
		multiple[i] = 2019*i;
	int ans = 0;
	for(i=1;i<=100;++i){
		string t = to_string(multiple[i]);
		size_t found = s.find(t, 0, t.length());
    	if (found != string::npos) 
        	ans ++;
	}
	cout<<ans<<"\n";
    
#ifndef LOCAL_DEFINE
    cerr << "Time elapsed: "<< 1e1 * clock() / CLOCKS_PER_SEC << " s.\n";
#endif // LOCAL_DEFINE
    return 0;
}

Compiler output:
a.cc: In function 'int main(int, const char**)':
a.cc:86:38: error: no matching function for call to 'std::__cxx11::basic_string<char>::find(std::string&, int, std::__cxx11::basic_string<char>::size_type)'
   86 |                 size_t found = s.find(t, 0, t.length());
      |                                ~~~~~~^~~~~~~~~~~~~~~~~~
In file included from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52,
                 from a.cc:1:
/usr/include/c++/14/bits/basic_string.h:2720:9: note: candidate: 'template<class _Tp> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::_If_sv<_Tp, typename __gnu_cxx::__alloc_traits<typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_CharT>::other>::size_type> std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(const _Tp&, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>]'
 2720 |         find(const _Tp& __svt, size_type __pos = 0) const
      |         ^~~~
/usr/include/c++/14/bits/basic_string.h:2720:9: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/basic_string.h:2691:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(const _CharT*, size_type, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 2691 |       find(const _CharT* __s, size_type __pos, size_type __n) const
      |       ^~~~
/usr/include/c++/14/bits/basic_string.h:2691:26: note:   no known conversion for argument 1 from 'std::string' {aka 'std::__cxx11::basic_string<char>'} to 'const char*'
 2691 |       find(const _CharT* __s, size_type __pos, size_type __n) const
      |            ~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/basic_string.h:2706:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(const std::__cxx11::basic_string<_CharT, _Traits, _Alloc>&, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 2706 |       find(const basic_string& __str, size_type __pos = 0) const
      |       ^~~~
/usr/include/c++/14/bits/basic_string.h:2706:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/basic_string.h:2740:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(const _CharT*, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 2740 |       find(const _CharT* __s, size_type __pos = 0) const _GLIBCXX_NOEXCEPT
      |       ^~~~
/usr/include/c++/14/bits/basic_string.h:2740:7: note:   candidate expects 2 arguments, 3 provided
/usr/include/c++/14/bits/basic_string.h:2758:7: note: candidate: 'std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::size_type std::__cxx11::basic_string<_CharT, _Traits, _Alloc>::find(_CharT, size_type) const [with _CharT = char; _Traits = std::char_traits<char>; _Alloc = std::allocator<char>; size_type = long unsigned int]'
 2758 |       find(_CharT __c, size_type __pos = 0) const _GLIBCXX_NOEXCEPT;
      |       ^~~~
/usr/include/c++/14/bits/basic_string.h:2758:7: note:   candidate expects 2 arguments, 3 provided