Language: C++

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

int main() {
  
  long long n, k;
  cin >> n >> k;
  
  if (n>k) {
    int s=n%k;
    if (s>k/2/*ポイント*/) cout << k-s << endl;
    else cout << s << endl;
  }
  
  else {
    if (n>k/2) cout << k-n << endl;
    else cout << n << endl;
  }
}

Compiler output:
a.cc:2:17: error: 'stdc' is not a namespace-name
    2 | using namespace stdc;
      |                 ^~~~
a.cc: In function 'int main()':
a.cc:7:3: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    7 |   cin >> n >> k;
      |   ^~~
      |   std::cin
In file included from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:146,
                 from a.cc:1:
/usr/include/c++/14/iostream:62:18: note: 'std::cin' declared here
   62 |   extern istream cin;           ///< Linked to standard input
      |                  ^~~
a.cc:11:28: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   11 |     if (s>k/2/*ポイント*/) cout << k-s << endl;
      |                            ^~~~
      |                            std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:11:43: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   11 |     if (s>k/2/*ポイント*/) cout << k-s << endl;
      |                                           ^~~~
      |                                           std::endl
In file included from /usr/include/c++/14/istream:41,
                 from /usr/include/c++/14/sstream:40,
                 from /usr/include/c++/14/complex:45,
                 from /usr/include/c++/14/ccomplex:39,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:127:
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:12:10: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   12 |     else cout << s << endl;
      |          ^~~~
      |          std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:12:23: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   12 |     else cout << s << endl;
      |                       ^~~~
      |                       std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:16:16: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   16 |     if (n>k/2) cout << k-n << endl;
      |                ^~~~
      |                std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:16:31: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   16 |     if (n>k/2) cout << k-n << endl;
      |                               ^~~~
      |                               std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~
a.cc:17:10: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   17 |     else cout << n << endl;
      |          ^~~~
      |          std::cout
/usr/include/c++/14/iostream:63:18: note: 'std::cout' declared here
   63 |   extern ostream cout;          ///< Linked to standard output
      |                  ^~~~
a.cc:17:23: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   17 |     else cout << n << endl;
      |                       ^~~~
      |                       std::endl
/usr/include/c++/14/ostream:744:5: note: 'std::endl' declared here
  744 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~