Main.cc: In function 'int main()':
Main.cc:6:5: error: 'cin' was not declared in this scope; did you mean 'std::cin'?
    6 |     cin >> r;
      |     ^~~
      |     std::cin
In file included from Main.cc:1:
/usr/include/c++/12.2.1/iostream:60:18: note: 'std::cin' declared here
   60 |   extern istream cin;           /// Linked to standard input
      |                  ^~~
Main.cc:10:5: error: 'cout' was not declared in this scope; did you mean 'std::cout'?
   10 |     cout << setprecision(5) << S <<endl;
      |     ^~~~
      |     std::cout
/usr/include/c++/12.2.1/iostream:61:18: note: 'std::cout' declared here
   61 |   extern ostream cout;          /// Linked to standard output
      |                  ^~~~
Main.cc:10:13: error: 'setprecision' was not declared in this scope; did you mean 'std::setprecision'?
   10 |     cout << setprecision(5) << S <<endl;
      |             ^~~~~~~~~~~~
      |             std::setprecision
In file included from Main.cc:2:
/usr/include/c++/12.2.1/iomanip:195:3: note: 'std::setprecision' declared here
  195 |   setprecision(int __n)
      |   ^~~~~~~~~~~~
Main.cc:10:36: error: 'endl' was not declared in this scope; did you mean 'std::endl'?
   10 |     cout << setprecision(5) << S <<endl;
      |                                    ^~~~
      |                                    std::endl
In file included from /usr/include/c++/12.2.1/iostream:39:
/usr/include/c++/12.2.1/ostream:688:5: note: 'std::endl' declared here
  688 |     endl(basic_ostream<_CharT, _Traits>& __os)
      |     ^~~~