Why doesn't this simple multiprocessing function work?

Question

I am just learning about multiprocessing in python. And when I am trying to run the code I receive these problems.

Code

from multiprocessing import Process, cpu_count


def counter1(num):
    count = 0
    while count < num:
        count += 1


def main():
    t1_start = perf_counter()
    processes = []
    for _ in range(4):
        p = Process(target=counter1, args=(10000,))
        p.start()
        processes.append(p)

    for process in processes:
        process.join()

    t1_stop = perf_counter()
    print("Elapsed time: {}".format(t1_stop - t1_start))


if __name__ == '__main__':
    main()

Problems

Traceback (most recent call last):
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\code.py", line 90, in runcode
    exec(code, self.locals)
  File "<input>", line 1, in <module>
  File "C:\Program Files\JetBrains\PyCharm 2021.3.3\plugins\python\helpers\pydev\_pydev_bundle\pydev_umd.py", line 198, in runfile
    pydev_imports.execfile(filename, global_vars, local_vars)  # execute the script
  File "C:\Program Files\JetBrains\PyCharm 2021.3.3\plugins\python\helpers\pydev\_pydev_imps\_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:/Users/Женя/PycharmProjects/test_loria/mp.py", line 54, in <module>
    main()
  File "C:/Users/Женя/PycharmProjects/test_loria/mp.py", line 43, in main
    p.start()
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\process.py", line 121, in start
    self._popen = self._Popen(self)
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py", line 224, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\context.py", line 327, in _Popen
    return Popen(process_obj)
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\popen_spawn_win32.py", line 93, in __init__
    reduction.dump(process_obj, to_child)
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\reduction.py", line 60, in dump
    ForkingPickler(file, protocol).dump(obj)
_pickle.PicklingError: Can't pickle <function counter1 at 0x000001FBC61EC040>: attribute lookup counter1 on __main__ failed
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\spawn.py", line 116, in spawn_main
    exitcode = _main(fd, parent_sentinel)
  File "C:\Users\Женя\AppData\Local\Programs\Python\Python310\lib\multiprocessing\spawn.py", line 126, in _main
    self = reduction.pickle.load(from_parent)
EOFError: Ran out of input

I have no idea what is going on. Because if I try to run the same code in another file, everything will be fine.