how to count selected objects 's number in editor?

it's better no need extra coding work if possible? If not,DO I NEED to create a script works in editor and invoke count function by menu item or sth? I'm newbie,if so, give the tutorial or link.

PS: the object may come from different parents and there's no specific tags or names , so Find*With Tag() stuff is not accessible!

thanks every one!

Regards!