In file included from /usr/include/c++/12/iostream:38,
                 from /in/foo.cc:5:
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h: In function 'int main()':
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:296:1: error: 'namespace' definition is not allowed here
  296 | namespace std
      | ^~~~~~~~~
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:329:1: error: 'namespace' definition is not allowed here
  329 | namespace std
      | ^~~~~~~~~
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:333:1: error: 'namespace' definition is not allowed here
  333 | namespace __gnu_cxx
      | ^~~~~~~~~
/usr/include/x86_64-linux-gnu/c++/12/bits/c++config.h:508:1: error: 'namespace' definition is not allowed here
  508 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/bits/memoryfwd.h:50:15: error: expected '=' before '__attribute__'
   50 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/memoryfwd.h:50:15: error: expected identifier before '__attribute__'
In file included from /usr/include/c++/12/bits/stringfwd.h:40,
                 from /usr/include/c++/12/iosfwd:39,
                 from /usr/include/c++/12/ios:38,
                 from /usr/include/c++/12/ostream:38,
                 from /usr/include/c++/12/iostream:39:
/usr/include/c++/12/bits/memoryfwd.h:50:14: error: expected ';' before '__attribute__'
   50 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/bits/memoryfwd.h:51:1: error: expected primary-expression before '{' token
   51 | {
      | ^
/usr/include/c++/12/bits/stringfwd.h:42:15: error: expected '=' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/stringfwd.h:42:15: error: expected identifier before '__attribute__'
/usr/include/c++/12/bits/stringfwd.h:42:14: error: expected ';' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/bits/stringfwd.h:43:1: error: expected primary-expression before '{' token
   43 | {
      | ^
In file included from /usr/include/features.h:489,
                 from /usr/include/x86_64-linux-gnu/bits/libc-header-start.h:33,
                 from /usr/include/stdio.h:27,
                 from /in/foo.cc:1:
/usr/include/wchar.h:79:1: error: expected unqualified-id before string constant
   79 | __BEGIN_DECLS
      | ^~~~~~~~~~~~~
In file included from /usr/include/c++/12/bits/postypes.h:40,
                 from /usr/include/c++/12/iosfwd:40:
/usr/include/c++/12/cwchar:62:1: error: 'namespace' definition is not allowed here
   62 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/cwchar:135:8: error: expected unqualified-id before string constant
  135 | extern "C++"
      |        ^~~~~
/usr/include/c++/12/cwchar:244:1: error: 'namespace' definition is not allowed here
  244 | namespace __gnu_cxx
      | ^~~~~~~~~
/usr/include/c++/12/cwchar:265:1: error: 'namespace' definition is not allowed here
  265 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/cwchar:280:1: error: 'namespace' definition is not allowed here
  280 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/bits/postypes.h:42:15: error: expected '=' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/postypes.h:42:15: error: expected identifier before '__attribute__'
/usr/include/c++/12/bits/postypes.h:42:14: error: expected ';' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/bits/postypes.h:43:1: error: expected primary-expression before '{' token
   43 | {
      | ^
/usr/include/c++/12/iosfwd:42:15: error: expected '=' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/iosfwd:42:15: error: expected identifier before '__attribute__'
/usr/include/c++/12/iosfwd:42:14: error: expected ';' before '__attribute__'
   42 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/iosfwd:43:1: error: expected primary-expression before '{' token
   43 | {
      | ^
In file included from /usr/include/c++/12/exception:38,
                 from /usr/include/c++/12/ios:39:
/usr/include/c++/12/bits/exception.h:40:8: error: expected unqualified-id before string constant
   40 | extern "C++" {
      |        ^~~~~
/usr/include/c++/12/exception:40:8: error: expected unqualified-id before string constant
   40 | extern "C++" {
      |        ^~~~~
In file included from /usr/include/c++/12/bits/exception_ptr.h:38,
                 from /usr/include/c++/12/exception:168:
/usr/include/c++/12/bits/cxxabi_init_exception.h:50:1: error: 'namespace' definition is not allowed here
   50 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/bits/cxxabi_init_exception.h:55:1: error: 'namespace' definition is not allowed here
   55 | namespace __cxxabiv1
      | ^~~~~~~~~
In file included from /usr/include/c++/12/typeinfo:36,
                 from /usr/include/c++/12/bits/exception_ptr.h:39:
/usr/include/c++/12/bits/hash_bytes.h:37:1: error: 'namespace' definition is not allowed here
   37 | namespace std
      | ^~~~~~~~~
/usr/include/c++/12/typeinfo:45:8: error: expected unqualified-id before string constant
   45 | extern "C++" {
      |        ^~~~~
In file included from /usr/include/c++/12/bits/exception_ptr.h:40:
/usr/include/c++/12/new:45:8: error: expected unqualified-id before string constant
   45 | extern "C++" {
      |        ^~~~~
/usr/include/c++/12/bits/move.h:38:15: error: expected '=' before '__attribute__'
   38 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/move.h:38:15: error: expected identifier before '__attribute__'
In file included from /usr/include/c++/12/bits/exception_ptr.h:43:
/usr/include/c++/12/bits/move.h:38:14: error: expected ';' before '__attribute__'
   38 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/bits/move.h:39:1: error: expected primary-expression before '{' token
   39 | {
      | ^
/usr/include/c++/12/type_traits:40:15: error: expected '=' before '__attribute__'
   40 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/type_traits:40:15: error: expected identifier before '__attribute__'
In file included from /usr/include/c++/12/bits/move.h:57:
/usr/include/c++/12/type_traits:40:14: error: expected ';' before '__attribute__'
   40 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/type_traits:41:1: error: expected primary-expression before '{' token
   41 | {
      | ^
/usr/include/c++/12/bits/move.h:59:15: error: expected '=' before '__attribute__'
   59 | namespace std _GLIBCXX_VISIBILITY(default)
      |               ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/move.h:59:15: error: expected identifier before '__attribute__'
/usr/include/c++/12/bits/move.h:59:14: error: expected ';' before '__attribute__'
   59 | namespace std _GLIBCXX_VISIBILITY(default)
      |              ^
      |              ;
/usr/include/c++/12/bits/move.h:60:1: error: expected primary-expression before '{' token
   60 | {
      | ^
/usr/include/c++/12/bits/exception_ptr.h:52:8: error: expected unqualified-id before string constant
   52 | extern "C++" {
      |        ^~~~~
In file included from /usr/include/c++/12/exception:169:
/usr/include/c++/12/bits/nested_exception.h:42:8: error: expected unqualified-id before string constant
   42 | extern "C++" {
      |        ^~~~~
/usr/include/c++/12/bits/char_traits.h:53:21: error: expected '=' before '__attribute__'
   53 | namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
      |                     ^~~~~~~~~~~~~~~~~~~
/usr/include/c++/12/bits/char_traits.h:53:21: error: expected identifier before '__attr