Language: C++

nclude"bits/stdc++.h"
#define REP(i,n) for(int i=0, i##_len=(n); i<i##_len; ++i)
#define REPS(i,n) for(int i=1, i##_len=(n); i<i##_len; ++i)
#define all(x) (x).begin(),(x).end()
using ll = long long;
using namespace std;
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; }
template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
#define INF 1e9
#define PI (acos(-1))
#define mod (int)1e9+7
int main() {
    int n;
    cin >> n;
    cout << 1000 * ceil((double)n / 1000) - n << endl;
    return 0;
}

Compiler output:
a.cc:1:1: error: 'nclude' does not name a type
    1 | nclude"bits/stdc++.h"
      | ^~~~~~
a.cc:9:22: error: 'size_t' has not been declared
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                      ^~~~~~
a.cc:9:65: error: 'N' was not declared in this scope
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                                                                 ^
a.cc:9:49: error: variable or field 'Fill' declared void
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                                                 ^~~~
a.cc:9:58: error: 'array' was not declared in this scope
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                                                          ^~~~~
a.cc:1:1: note: 'std::array' is defined in header '<array>'; this is probably fixable by adding '#include <array>'
  +++ |+#include <array>
    1 | nclude"bits/stdc++.h"
a.cc:9:65: error: 'N' was not declared in this scope
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                                                                 ^
a.cc:9:69: error: expected primary-expression before 'const'
    9 | template<typename A, size_t N, typename T> void Fill(A (&array)[N], const T &val) { std::fill( (T*)array, (T*)(array+N), val ); }
      |                                                                     ^~~~~
a.cc: In function 'int main()':
a.cc:15:5: error: 'cin' was not declared in this scope
   15 |     cin >> n;
      |     ^~~
a.cc:1:1: note: 'std::cin' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
  +++ |+#include <iostream>
    1 | nclude"bits/stdc++.h"
a.cc:16:5: error: 'cout' was not declared in this scope
   16 |     cout << 1000 * ceil((double)n / 1000) - n << endl;
      |     ^~~~
a.cc:16:5: note: 'std::cout' is defined in header '<iostream>'; this is probably fixable by adding '#include <iostream>'
a.cc:16:20: error: 'ceil' was not declared in this scope
   16 |     cout << 1000 * ceil((double)n / 1000) - n << endl;
      |                    ^~~~
a.cc:16:50: error: 'endl' was not declared in this scope
   16 |     cout << 1000 * ceil((double)n / 1000) - n << endl;
      |                                                  ^~~~
a.cc:1:1: note: 'std::endl' is defined in header '<ostream>'; this is probably fixable by adding '#include <ostream>'
  +++ |+#include <ostream>
    1 | nclude"bits/stdc++.h"