If a Python file is part of a library, all of its code runs the first time it is imported. This can be problematic if the file is a program on its own that, for example, interacts with the user—the importing code probably does not want any of those user interactions. Therefore, Python defines a special variable, __name__ that is set to the string '__main__' only in the file that is actually being run, not in any imported files. Python files can check this variable and only run as a program if it is set to '__main__'.

Fill in the placeholders so that file detects that it is the main program.